Fish sauce over leafy vegetable (8)
I believe the answer is:
pilchard
'fish' is the definition.
(pilchard is a kind of fish)
'sauce over leafy vegetable' is the wordplay.
'sauce' becomes 'lip' (I've seen this before).
'over' is a reversal indicator.
'leafy vegetable' becomes 'chard' (chard is a kind of leafy vegetable).
'lip' reversed gives 'pil'.
'pil'+'chard'='PILCHARD'
(Other definitions for pilchard that I've seen before include "Fish of herring family" , "'Small fatty fish, usually canned (8)'" , "Edible herring relative" , "Small marine food fish" , "type of fish" .)