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

Trim about ¼ inch from tops of bell peppers and remove stems, ribs, and seeds. Fill a baking dish with ½ inch of water and place peppers upside down. Cover with foil and bake for 20 minutes.

Heat olive oil in a large skillet over medium-high heat. Add chopped onion and sauté for 3-4 minutes. Push onions to the side, add ground beef, season with salt and pepper, and sear until browned, about 3 minutes.

Break up the beef, toss with onions, cook for 2 minutes. Add minced garlic and cook until beef is cooked through, about 1 minute. Drain excess fat.

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

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

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