Green garnish (5)
I believe the answer is:
cress
'green garnish' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for cress that I've seen before include "Salad sprouts" , "Food item" , "Salad vegetable" , "Plant with pungent leaves used in salads" , "Plant with leaves used in salad or as garnish" .)