Prepare the Peppers: Preheat oven to 375°F (190°C). Wash bell peppers and remove tops, seeds, and membranes. Brush the outer surface with olive oil and place them upright in a baking dish.
Prepare the Filling (for both versions):
Heat olive oil in a skillet over medium heat. Sauté onions and garlic until softened.
For classic: Add ground meat, cook until browned, then stir in diced tomatoes, rice, seasoning, salt, and pepper.
For vegetarian: Stir in beans, quinoa or lentils, diced tomatoes, cumin, paprika, salt, and pepper. Cook for a few minutes.
Stuff and Bake: Spoon the filling into each bell pepper. Pour tomato sauce over each pepper and cover with foil. Bake for 30 minutes. Remove foil, sprinkle cheese on top, and bake for an additional 10 minutes until cheese is melted and golden.