Lightly oil grill and preheat to medium high.Advertisement
In a small skillet, heat vegetable oil. Saute onion and celery until tender. Stir in hot sauce and mustard and mix all together. Remove from heat.
Cut pockets into chicken breasts and stuff with onion mixture. Saute chicken in skillet 2 to 3 minutes each side, until lightly browned. Remove from skillet and grill over medium high heat for 10 to 15 minutes on each side, or until juices run clear. Serve with remainder of onion mixture as a sauce/topping.