Fish steak that's cooked (5)
I believe the answer is:
skate
'fish' is the definition.
(skate is a kind of fish)
'steak that's cooked' is the wordplay.
'that's cooked' indicates anagramming the letters (letters cooked into a new form).
'steak' with letters rearranged gives 'SKATE'.
(Other definitions for skate that I've seen before include "Recite Keats badly to the fish" , "A ray; slide smoothly" , "Complete, 19-less" , "Ice-gliding blade; fish" , "Cartilaginous fish" .)