Dieter’s lunch (5)
I believe the answer is:
salad
'dieter's lunch' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for salad that I've seen before include "Mainly raw cold dish" , "Cold dish of raw vegetables" , "Raw greens, mainly" , "One may well be green" , "Cold vegetable dish" .)