Monkey with one's food (6)
I believe the answer is:
scampi
'food' is the definition.
(scampi is a kind of food)
'monkey with one's' is the wordplay.
'monkey' becomes 'scamp' (both can mean a mischievous child).
'with' means one lot of letters go next to another.
'one' becomes 'i' (Roman numeral).
'scamp'+'i'='SCAMPI'
(Other definitions for scampi that I've seen before include "Prawn dish" , "Breaded prawns" , "Tasty prawns in batter" , "Dish of fried shrimps or prawns" , "Crumby seafood dish" .)