Preheat your oven to 375°F (190°C).
In a large skillet over medium heat, cook the ground beef or turkey until browned. Drain any excess fat.
Add the diced onions and minced garlic to the skillet. Sauté for 2-3 minutes until the onions are translucent.
Stir in the diced bell peppers and cook for an additional 3-4 minutes until they start to soften.
Add the cooked rice, diced tomatoes (with their juice), tomato sauce, oregano, basil, salt, and black pepper. Mix well and let it simmer for about 5 minutes, allowing the flavors to meld.
Transfer the mixture to a greased 9x13 inch (23x33 cm) baking dish, spreading it evenly.
Sprinkle the shredded cheese over the top of the casserole.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly, and the casserole is heated through.
Remove from the oven and let it rest for a few minutes before serving.
Serve your Stuffed Pepper Casserole with a side salad or enjoy it as is!