Shellfish that’s uncooked put into empty pan (5)
I believe the answer is:
prawn
'shellfish' is the definition.
(thesaurus)
'uncooked put into empty pan' is the wordplay.
'uncooked' becomes 'raw' ('raw' can be similar in meaning to 'uncooked').
'put into' is an insertion indicator.
'empty' means to remove the middle letters.
'pan' with its centre taken out is 'pn'.
'raw' going within 'pn' is 'PRAWN'.
'that's' acts as a link.
(Other definitions for prawn that I've seen before include "Shrimp-like crustacean" , "Cocktail item" , "Small, edible crustacean" , "Cocktail ingredient" , "Shellfish" .)