Salad food (7)
I believe the answer is:
This clue is a double definition.
'salad' is the first definition.
(I've seen this before)
'food' is the second definition.
(lettuce is a kind of food)
(Other definitions for lettuce that I've seen before include "Plant for the salad bowl" , "Leafy vegetable" , "eg Webbs wonder" , "Salad green" , "Garden plant with edible green leaves, good in salads" .)