Cut tops off peppers and remove seeds. Place peppers in a large saucepan and cover with water. Bring to a boil; cook for 3 minutes. Drain and immediately place in ice water; invert on paper towels., In a small skillet, cook beef and onion over medium heat until meat is no longer pink; drain. Remove from the heat. Stir in 1 cup tomato sauce, rice, salt, garlic powder and pepper. Spoon into peppers. , Place in an ungreased shallow 2-qt. baking dish. Drizzle with remaining tomato sauce. Cover and bake at 350° for 25-30 minutes or until peppers are tender.