Rolls topped with unwrapped spam or fish (4)
I believe the answer is:
parr
'fish' is the definition.
(I know that parr is a type of young fish)
'rolls topped with unwrapped spam' is the wordplay.
'rolls' becomes 'RR' (Rolls Royce).
'topped with' is a charade indicator (letters next to each other).
'unwrapped' means to look at the middle letters (the letters which wrap the word are removed).
The centre of 'spam' is 'pa'.
'rr' after 'pa' is 'PARR'.
'or' is the link.
(Other definitions for parr that I've seen before include "Fish" , "survivor of the decapitator?" , "Catherine --, last wife of Henry VIII" , "Wife surviving" , "Henry VIII's sixth queen" .)