With knife, slice 1/2-inch off top of red peppers. Remove seeds and ribs. Coarsely chop tops and set aside.
In medium bowl, combine 2 cups sauce, 1 cup cheese, chopped red peppers and remaining ingredients. Evenly stuff peppers.
In 4-1/2-quart slow cooker sprayed with no-stick cooking spray, arrange peppers. Top with remaining sauce. Cook covered on LOW 8 to 10 hours or HIGH 4 to 6 hours. Sprinkle with remaining 1 cup cheese and cook covered an additional 10 minutes or until cheese is melted. To serve, slice peppers in half.