1. Preheat oven to 375°F (190°C). Boil the jumbo pasta shells in salted water until just al dente. Drain and set aside.
2. In a skillet, cook ground beef until browned. Add garlic, Italian seasoning, salt, and pepper. Stir and remove from heat.
3. Mix ricotta, 1 cup mozzarella, and 1/2 cup Parmesan in a bowl. Combine with the cooked beef mixture.
4. Spread 1 cup marinara sauce on the bottom of a baking dish. Stuff each shell with the beef and cheese mixture, then place them in the dish.
5. Pour remaining marinara sauce over the shells. Sprinkle with the rest of the mozzarella and Parmesan.
6. Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 10 minutes until bubbly and golden.
7. Garnish with fresh parsley and serve warm.