1. Preheat oven to 375°F (190°C). Slice off the tops of the bell peppers and remove seeds and membranes.
2. Bring a large pot of water to a boil and blanch the peppers for 3 minutes. Drain and set aside.
3. In a skillet, heat olive oil over medium heat. Sauté onion and garlic until softened. Add ground beef, cooking until browned.
4. Stir in cooked rice, diced tomatoes, half the tomato sauce, Italian seasoning, salt, and pepper. Cook for 5 minutes.
5. Stuff each bell pepper with the beef and rice mixture. Place them upright in a baking dish.
6. Spoon additional tomato sauce over the tops of the peppers. Cover with foil and bake for 30 minutes. Remove foil and bake for 10 more minutes.
7. Garnish with fresh parsley and serve warm.