PREHEAT grill or grill pan to medium heat and grease with olive oil cooking spray. Cook chicken breasts 8-10 minutes each side. Allow chicken to cool 5 minutes. Slice into small pieces.
COMBINE chicken, apples, celery, grapes and pecans in a large mixing bowl. Stir in mayonnaise, mustard, sea salt and black pepper. Refrigerate until serving. Spoon over lettuce leaves.