Boil chicken for 20 minutes or until no longer pink inside. Chop chicken into small bite-size pieces. Slice celery. Chop onion and bell pepper. Chop or press garlic.
Melt butter in 12" skillet over medium heat. Add celery, onion, bell pepper and garlic to skillet. Cook and stir 3-4 minutes or until vegetables are tender. Add chicken, barbecue sauce, salt and black pepper.
Cook 5 minutes or until mixture comes to a boil, stir occasionally. Serve on buns.