Place The Chicken In A Large Resealable Plastic Bag; Add Barbecue Sauce. Seal The Bag And Turn To Coat. Refrigerate Overnight. Grill Chicken, Covered, Over Medium-Hot Heat For 6-8 Minutes On Each Side Or Until Juices Run Clear. Cool; Cover And Refrigerate Chicken Until Chilled. Chop Chicken; Place In A Bowl. Stir In The Mayonnaise, Onion, Celery, Salt And Pepper Flakes. Serve On Rolls With Tomato And Lettuce.