Bun might initially work for pickled herring (7)
I believe the answer is:
rollmop
'pickled herring' is the definition.
(I've seen this before)
'bun might initially work' is the wordplay.
'bun' becomes 'roll' ('roll' can be a synonym of 'bun').
'initially' suggests taking the first letters.
'work' becomes 'op' (abbreviation for opus).
The initial letter of 'might' is 'm'.
'roll'+'m'+'op'='ROLLMOP'
'for' is the link.
(Other definitions for rollmop that I've seen before include "Ex-swimmer preserved" , "Herring pickled in spiced vinegar" , "seafood?" , "savoury dish" , "Pickled herring on a stick" .)