Preheat oven to 350°F (175°C) and grease a loaf pan.
Prepare Peppers: Cut the tops off 6 bell peppers, remove seeds and membranes.
Cook Filling: In a skillet, sauté 1 diced onion and 2 minced garlic cloves until soft. Add 1 pound ground beef and cook until browned. Season with salt, pepper, and 1 teaspoon Italian seasoning.
Add Rice and Tomatoes: Stir in 1 cup cooked rice and 1 can (14.5 oz) diced tomatoes. Cook for a few more minutes.
Stuff Peppers: Spoon the beef mixture into the hollowed-out peppers, packing tightly.
Arrange in Dish: Place stuffed peppers upright in a baking dish. Add 1/2 cup water or broth to the bottom of the dish.
Top with Cheese: Sprinkle shredded mozzarella or cheddar cheese on top of each stuffed pepper.
Bake: Cover with foil and bake for 30 minutes. Remove foil and bake for an additional 10-15 minutes until peppers are tender and cheese is melted.
Serve: Let cool slightly before serving. Enjoy your stuffed peppers!