Step 1

Remove tops, membranes and seeds from peppers. Chop enough tops to make 1/3 cup; set aside. If necessary, cut a thin slice from the bottom of each pepper so they sit flat. In a medium bowl, stir together rice and undrained beans; spoon into peppers. Pour tomato sauce into the bottom of a 4 1/2-, 5- or 6-quart slow cooker; stir in reserved chopped pepper and onion. Place peppers, filled-side up, in cooker.

Step 2

Cover and cook on Low for 6 to 6 1/2 hours or on High for 3 to 3 1/2 hours.

Step 3

To serve, transfer peppers to serving plate and cut in half, if desired. Spoon tomato sauce over peppers and sprinkle with cheese.