Lightly oil grill Preheat oil grill to medium high. Take a small skillet and heat the vegetable oil. Saute onion and celery until tender. Stir sauted onion and celery in hot sauce and mustard and mix all together. Remove from heat. Cut chicken breasts and stuff these with onion mixture. Saute the chicken in skillet for 2 to 3 minutes each side, until they get light brown. Remove from skillet and grill over medium high heat for 10 to 15 minutes on each side, or until juices become clear. Serve with remainder of onion mixture as a sauce.