Preheat oven to 400°F. Cook rice according to package instructions.

Trim about 1/4-inch from tops of bell peppers, remove stems, ribs, and seeds. Fill a baking dish with 1/2-inch of water.

Place peppers upside down in water, cover with foil, and bake for 20 minutes.

Heat olive oil in a large skillet over medium-high heat. Add onion and sauté for 3-4 minutes. Add ground beef, season with salt and pepper, and cook until browned, about 3 minutes.

Break up the beef, add garlic, cook for 1 minute. Drain excess fat.

Stir in tomatoes, half of the tomato sauce, cooked rice, parsley, Italian seasoning, salt, and pepper.

Reduce oven temperature to 350°F. Turn peppers upright, season insides lightly with salt, and fill with beef mixture. Pour remaining tomato sauce over peppers. Cover with foil and bake for 20 minutes.

Remove from oven, sprinkle with mozzarella cheese, and bake uncovered until peppers are tender, about 10-20 minutes. Garnish with parsley and serve warm.