Character told to clean fish fillet (7)
I believe the answer is:
rollmop
'fish fillet' is the definition.
(type of herring fillet)
'character told to clean' is the wordplay.
'character' becomes 'role' (synonyms).
'told' indicates a 'sounds like' (homophone) clue.
'to clean' becomes 'mop' (mopping is a kind of cleaning).
'role' sounds like 'roll'.
'roll'+'mop'='ROLLMOP'
(Other definitions for rollmop that I've seen before include "Dish of herring fillet" , "Pickled herring on a stick" , "Curled-up herring fillet" , "Pickled fillet of raw herring" , "Fish" .)