Beefy Cowboy Beans

1 1/2 pounds ground beef
1 medium onion, chopped
1 red or green bell pepper, cut into 1/2-inch pieces
1 (16 ounce) can baked beans
1 (15 1/2 ounce) can Great Northern beans, rinsed and drained
1/4 cup tomato catsup
1/4 cup Heinz 57