Preheat your oven to 375°F (190°C).
Slice the tops off the bell peppers and remove the seeds and membranes, creating a hollow cavity for the filling.
In a large skillet, cook the ground beef or turkey over medium heat until browned and crumbled, about 5-7 minutes. Drain any excess fat.
Add the chopped onion and minced garlic to the skillet. Sauté for 2-3 minutes, or until the onion is translucent.
Stir in the cooked rice, tomato sauce, oregano, basil, salt, and black pepper. Mix well and let the filling simmer for 5 minutes, stirring occasionally.
Arrange the hollowed-out bell peppers in a baking dish. Spoon the filling mixture evenly into the bell pepper cavities, packing it in gently.
Top each stuffed pepper with a generous amount of shredded mozzarella cheese.
Bake the stuffed peppers in the preheated oven for 30-35 minutes, or until the peppers are tender and the cheese is melted and bubbly.
Remove the stuffed peppers from the oven and let them cool for a few minutes before serving.