In 12-inch nonstick skillet, cook ground beef, celery, bell pepper and onion over medium-high heat 5 to 7min., stirring occasionally, until beef is thoroughly cooked; drain.
Reduce heat to medium. Stir in all remaining ingredients except buns, cook 15 to 20 min. longer or until mixture is bubbly and vegetables are tender, stiring occasionally. Spoon beef mixture into buns.