1. Preheat oven to 350 degrees F. Grease a 9x13 inch baking dish.
2. In a large skillet over medium-high heat, cook beef and onion until beef is no longer pink. Drain excess fat. Stir in rice, tomatoes, garlic powder, Italian seasoning, salt, and black pepper.
3. Stuff each pepper half with beef mixture. Place in prepared baking dish.
4. Bake for 30 minutes. Sprinkle with cheese and bake for an additional 5 minutes, or until cheese is melted.