1. In a small saucepan, melt the butter over moderate flame.
2. Add the celery, onion, green pepper and garlic powder. SautÃ© until limp.
3. Tip in the barbecue sauce and the chicken. Stir well to mix.
4. Allow the mixture to heat through, stirring to prevent it from sticking to the pan.
5. Spoon the hot mixture on the buns and serve hot.