Sides of pan filled with uncooked seafood (5)
I believe the answer is:
prawn
'seafood' is the definition.
(prawn is a kind of seafood)
'sides of pan filled with uncooked' is the wordplay.
'sides of' means to remove the middle letters (only the letters on the sides remain).
'filled with' is an insertion indicator.
'uncooked' becomes 'raw' (similar in meaning).
'pan' with its middle taken out is 'pn'.
'pn' enclosing 'raw' is 'PRAWN'.
(Other definitions for prawn that I've seen before include "Cocktail ingredient" , "Cocktail item" , "Bit of seafood" , "Small tasty crustacean, nice in cocktail" , "Large shrimp" .)