Wash the bell peppers under cool water, cut the tops off, and remove seeds and membranes. Set aside.
In a large skillet, heat olive oil over medium heat. Sauté chopped onion and minced garlic for 3-4 minutes until translucent.
Add ground beef or turkey to the skillet and cook until browned, about 5-7 minutes. Drain excess fat.
Stir in cooked rice, diced tomatoes, Italian seasoning, salt, and black pepper. Cook for another 2-3 minutes.
Stuff each bell pepper with the meat and rice mixture, packing gently. Place them upright in a baking dish.
Cover the baking dish with aluminum foil and bake in a preheated oven at 375°F for 25 minutes.
Remove the foil, sprinkle cheese on top of each pepper, and bake for an additional 10-15 minutes until cheese is melted.
Let cool for a few minutes before serving.