Place the chicken in a large resealable plastic bag.
Add barbecue sauce.
Seal the bag and turn to coat.
Grill chicken, covered, over medium hot heat for 6 to 8 minutes on each side or until a meat thermometer reads 170°.
Cover and refrigerate chicken until chilled.
Place in a large bowl.
Stir in the mayonnaise, onion, celery, salt and pepper flakes.
Serve on rolls with lettuce and tomato.