1. Preheat the oven to 375°F and lightly grease a baking dish.

2. Slice the tops off the bell peppers and remove the seeds and membranes. Set the peppers upright in the baking dish.

3. Heat the olive oil in a large skillet over medium heat. Add the onion and cook until softened, then add the garlic and stir for about 30 seconds.

4. Add the ground beef and cook until browned, breaking it up as it cooks. Drain excess grease if needed.

5. Stir in the cooked rice, half of the tomato sauce, Italian seasoning, salt, and black pepper. Cook for 2 to 3 minutes until everything is well combined.

6. Spoon the filling into each pepper, packing it in gently. Pour the remaining tomato sauce around and lightly over the peppers.

7. Cover the dish with foil and bake for 30 to 35 minutes.

8. Remove the foil, top each pepper with mozzarella cheese, and bake uncovered for 10 to 15 minutes more until the cheese is melted and the peppers are tender.

9. Sprinkle with fresh parsley, let rest for a few minutes, and serve warm.