Zucchini, Mushroom & Tuna Baked Egg Casserole

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This Zucchini, Mushroom & Tuna Baked Egg Casserole transforms simple pantry and garden ingredients into a comforting, sliceable dish that works equally well for breakfast, brunch, lunch, or a light dinner. At its core is a custardy blend of eggs, milk, and flour seasoned with salt and pepper, which sets up around thinly sliced zucchini to form a tender “crust.” A sautéed mélange of onion, garlic, carrot, celery, bell pepper, and mushrooms lends aromatic depth and vegetable goodness. Canned tuna adds satisfying ocean‑fresh protein, while a final shower of grated cheese melts into golden pockets of richness. Once baked to bubbling perfection and topped with a fresh yogurt‑mayo cucumber sauce, each forkful delivers a symphony of textures—silky egg, soft vegetables, flaky tuna, and crisped edges—and flavors that feel at once rustic and refined.

Preparation, Cook, and Total Times

Prep Time: 25 minutes
Cook Time: 30 minutes
Total Time: 55 minutes

YIELD

Serves 6 generously as a main course or 8–10 as a hearty appetizer.

CUISINE

A fusion of Mediterranean and Eastern European influences, marrying the concept of a vegetable frittata with layered casseroles and savory “cakes.”

A Full List of Ingredients

Egg Casserole Base:

4 large eggs, at room temperature
100 ml (⅓ cup + 1 Tbsp) milk

3 Tbsp (24 g) all‑purpose flour
Salt, to taste (about 1 tsp)
Freshly ground black pepper, to taste (about ½ tsp)

Vegetable & Mushroom Layer:

1 zucchini (about 200 g), ends trimmed and thinly sliced into rounds

2 Tbsp vegetable oil, divided
1 onion, finely chopped (about 150 g)
1 garlic clove, minced

1 carrot, peeled and grated
1 celery stalk, finely diced
1 bell pepper, seeded and diced (any color)

200 g (7 oz) mushrooms, wiped and sliced
Salt and pepper, to taste

Protein & Cheese Layer:

1 (180 g) can tuna in water, drained and flaked
150 g (5.3 oz) cheese, grated (e.g., mozzarella, cheddar, or a blend)

Creamy Cucumber‑Yogurt Sauce:

2 Tbsp plain yogurt

1 Tbsp mayonnaise
1 small cucumber (about 100 g), peeled, seeded, and finely diced
1 garlic clove, minced

Salt and pepper, to taste

Step‑by‑Step Cooking Directions

Preheat & Prepare Pan
Preheat your oven to 180 °C (350 °F). Lightly grease a 20×20 cm (8×8 inch) square baking dish or similarly sized casserole pan with a thin coat of vegetable oil.
Mix Egg Batter
In a medium mixing bowl, whisk together the 4 eggs, milk, flour, salt, and pepper until no lumps remain. The batter should be smooth and slightly thickened. Set aside to allow the flour to hydrate.

Slice the Zucchini
Wash the zucchini, trim off the ends, and slice into approximately 3 mm‑thick rounds. Lay the slices on paper towels and sprinkle lightly with salt. Let sit for 5 minutes to draw out excess moisture, then pat dry with another paper towel. This ensures your casserole isn’t watery.
Sauté Aromatics & Veggies
Heat 1 Tbsp vegetable oil in a large skillet over medium heat. Add the chopped onion and sauté until translucent, about 3–4 minutes. Stir in the minced garlic and cook for another 30 seconds until fragrant.
Add the grated carrot and diced celery, cooking for 2 minutes until they begin to soften. Stir in the diced bell pepper and cook for another 2 minutes. Season lightly with salt and pepper as you go. Transfer this vegetable mixture to a bowl and set aside.
Cook Mushrooms
In the same skillet, add the remaining 1 Tbsp oil over medium‑high heat. Add the sliced mushrooms and cook, stirring occasionally, until they release their liquid and become golden brown, about 5–7 minutes. Season with a pinch of salt and pepper. Remove from heat and add to the vegetable bowl, stirring to combine.

Layer Zucchini and Fillings
Arrange half of the zucchini rounds in a single layer on the bottom of the prepared baking dish, overlapping slightly. They will form the base “crust.”
Spoon half of the sautéed vegetable‑mushroom mixture over the zucchini, spreading evenly. Top with the flaked tuna, distributing it uniformly. Sprinkle half of the grated cheese over the tuna.
Pour half of the egg batter evenly over these layers, allowing it to seep between the zucchini slices.
Repeat: layer the remaining zucchini, vegetables, tuna, cheese, and egg batter, finishing with cheese on top.
Bake the Casserole
Place the dish in the preheated oven and bake for 25–30 minutes, or until the top is golden brown, the egg is fully set, and a knife inserted in the center comes out clean. If the top browns too quickly, tent loosely with foil for the last 10 minutes.
Prepare the Cucumber‑Yogurt Sauce
While the casserole bakes, combine the yogurt, mayonnaise, diced cucumber, minced garlic, and a pinch of salt and pepper in a small bowl. Stir until smooth and refrigerate until serving.

Rest & Serve
Remove the casserole from the oven and let it rest for 5 minutes to firm up. Cut into squares and serve each portion with a dollop of the creamy cucumber‑yogurt sauce on the side or drizzled on top.

Nutritional Information

(Per serving, based on 8 servings; approximate)

Calories: 295 kcal
Total Fat: 17 g (Saturated Fat 7 g)
Cholesterol: 200 mg

Sodium: 620 mg
Total Carbohydrates: 12 g (Dietary Fiber 2 g; Sugars 3 g)
Protein: 22 g

The Origins and Popularity of the Recipe

Egg‑based bakes date back centuries in cuisines around the world—from Spanish tortilla to Italian frittata. These humble dishes showcase eggs’ binding power and adaptability, incorporating vegetables, meats, and cheeses. The concept of layering ingredients into a casserole emerged in Eastern European comfort‑food traditions, offering a make‑ahead, shareable meal. Adding canned tuna reflects modern pantry‐friendly cooking, while zucchini and mushrooms nod to summer‑harvest produce. The resulting dish is a synergy of convenience and tradition, widely adopted in home kitchens for its ease, flexibility, and nutritious profile.

Reasons Why You’ll Love the Recipe

Balanced Nutrition: Protein, vegetables, and modest carbs in one dish.

Make‑Ahead Ease: Assemble the night before and bake fresh in the morning.
Kid‑Friendly: Mild flavors and cheesy texture appeal to all ages.
Customizable: Swap tuna for chicken, omit dairy for vegan cheese alternatives, or add herbs to suit your palate.

Minimal Cleanup: One pan plus a small bowl for the sauce.

Health Benefits

High Protein: Eggs and tuna support muscle maintenance and satiety.
Vitamin‑Rich: Zucchini, carrots, peppers, and mushrooms provide vitamins A, C, and antioxidants.

Bone Health: Dairy in the cheese supplies calcium and vitamin D.
Probiotic Boost: If using live‑culture yogurt in the sauce.
Low Carb Option: Omit carrots or use low‑fat cheese for reduced calories.

Serving Suggestions

Fresh Salad: Pair with a crisp mixed‑greens salad dressed in lemon vinaigrette.
Grain Side: Serve with quinoa or barley tossed in olive oil and herbs.
Soup Pairing: Accompany with a tomato bisque or chilled cucumber soup.

Toast Points: Offer toasted baguette slices for scooping.
Wine Pairing: A dry rosé or unoaked Chardonnay complements the casserole’s mild flavors.

Common Mistakes to Avoid

Skipping Zucchini Drainage: Excess moisture leads to a soggy base; always salt and pat dry.

Undercooking Vegetables: Make sure mushrooms and other veggies are well‑sautéed to concentrate flavors.
Pouring Batter Too Quickly: Allow batter to rest briefly so flour hydrates, then pour gently to maintain layers.
Overbaking: Watch the casserole toward the end to prevent the cheese from burning.

Pairing Recommendations

Beer: A light lager or wheat beer cleanses the palate.
Non‑Alcoholic: Sparkling mineral water with a twist of lime.
Sauces: Offer a side of salsa verde or harissa for a spicy kick.

Cheese Board: Serve alongside mild brie or goat cheese with fruit preserves.

Cooking Tips

Room‑Temp Eggs: Ensures even mixing and smoother texture.
Even Slicing: Use a mandoline for uniform zucchini rounds that bake evenly.

Gentle Stirring: Fold fillings lightly to preserve air in the egg batter.
Monitoring Oven: Rotate the pan halfway to compensate for hot spots.

Variations to Try

Chicken & Broccoli: Substitute tuna with cooked chicken and add steamed broccoli florets.

Mexican‑Style: Add diced jalapeños, corn, black beans, and top with pepper jack cheese; serve with salsa and sour cream.
Mediterranean: Fold in artichoke hearts, sun‑dried tomatoes, and feta cheese, and garnish with fresh basil.
Keto Adaptation: Skip flour, use extra eggs, and add almond flour or coconut flour for binding.

Vegan Option: Use chickpea flour “egg” batter, plant‑based milk, vegan cheese, and tofu instead of tuna.

Similar Recipes to Try

Spanish Tortilla – Potato and onion frittata cooked in a skillet.
Italian Frittata di Zucchine – Zucchini and Parmesan egg bake finished under broiler.

Quiche Lorraine – Savory tart with eggs, cream, and bacon in a pastry shell.
Mushroom Strata – Layered bread, eggs, and mushroom casserole, perfect for brunch.

Ingredient Spotlight

Zucchini: Low in calories and high in water content, zucchini provides moisture and body to the egg base. Rich in vitamin C and potassium, it pairs beautifully with eggs and cheese for a balanced taste profile.

Conclusion

This Zucchini, Mushroom & Tuna Baked Egg Casserole offers a versatile, nutritious, and crowd‑pleasing recipe that brings restaurant‑quality flair to the home kitchen. With minimal preparation, you can layer flavors and textures—crisp zucchini, sautéed veg, flaky tuna, and melted cheese—into a single, satisfying dish. Whether served for family brunch, weeknight dinner, or as an impressive appetizer, it promises simplicity in cooking and sophistication on the plate.

10 Comprehensive FAQs

1. Can I prepare this casserole ahead of time?
Yes—you can assemble the layers in the baking dish, cover tightly, and refrigerate for up to 24 hours. Bake directly from the fridge, adding 5 minutes to the cook time.

2. How do I prevent the zucchini from making the casserole watery?
Salt the zucchini slices and let sit for 5–10 minutes, then pat them dry thoroughly with paper towels before layering.

3. Can I use frozen mushrooms or spinach instead of fresh?
Yes—thaw and drain thoroughly, then sauté to remove excess moisture before incorporating.

4. My casserole is too dry—what can I add?
Stir an additional 2 Tbsp of cream or milk into the egg batter, or drizzle a little olive oil over the top before baking.

5. How do I make this dish gluten‑free?
Substitute the flour with a gluten‑free 1:1 baking blend or rice flour and ensure all other ingredients are certified gluten‑free.

6. Can I omit the tuna for a vegetarian version?
Absolutely—simply leave out the tuna or replace it with cooked chickpeas or crumbled tofu for protein.

7. My cheese burned before the casserole was done—any tips?
Cover loosely with foil for the first 20 minutes of baking, then remove foil to finish browning in the last 10 minutes.

8. What cheese works best?
Mozzarella and cheddar blend melts smoothly, but you can experiment with Gruyère, Swiss, or plant-based cheeses for different flavors.

9. How should I reheat leftovers?
Reheat individual portions in a 180 °C (350 °F) oven for 8–10 minutes or in a nonstick skillet over low heat to retain crisp edges.

10. Can I add herbs or spices to customize?
Yes—try adding chopped fresh basil, thyme, or a pinch of smoked paprika to the egg batter or vegetable layer for extra aroma and depth.