Cook ground beef in 12-inch skillet over medium heat until no longer pink. Add onion and bell pepper; continue cooking 3-4 minutes or until vegetables are softened. Add all remaining ingredients except bread and cheese. Reduce heat to low; cook 5-10 minutes or until thickened.
Place bread onto ungreased baking sheet; broil 4 to 6 inches from heat, turning once, 4-6 minutes or until toasted. Top each with 1 slice cheese; continue broiling until melted. Top each with 1/2 cup beef mixture and 1 slice cheese; continue broiling 1 minute or until melted. Serve hot.