Mixture of diced apples, celery, walnuts and mayonnaise served on a bed of lettuce (7,5)
I believe the answer is:
waldorf salad
(Other definitions for waldorf salad that I've seen before include "Vegetarian dish of celery, apples, walnuts and mayonnaise" , "Apples, celery, walnuts and mayo" , "eats" , "Mix of apples, walnuts, celery, etc" .)