Cut enough off of the bottom of each onion to leave a flat surface. Carve out the onions, leaving a about a 1/2 inch thick shell. Chop
the carved out portion of the onions and set aside. Grill
the onion shells over medium-high heat, about 5 minutes or until tender. In a bowl, combine celery, Creole seasoning, black pepper, lemon juice and mayonnaise. Stir in the tuna. Spoon mixture into onion shells. Serve with fruit and crackers, if desired.