Seafood for rascal on island (6)
I believe the answer is:
scampi
'seafood' is the definition.
(type of seafood)
'rascal on island' is the wordplay.
'rascal' becomes 'scamp' (synonyms).
'on' is a charade indicator (letters next to each other).
'island' becomes 'i' (geographical abbreviation).
'scamp'+'i'='SCAMPI'
'for' acts as a link.
(Other definitions for scampi that I've seen before include "Fried seafood" , "Crumby seafood dish" , "Crumbed prawns" , "Shellfish" , "Cooked Norway lobsters" .)