Prawns occasionally cooked in this? (3)
I believe the answer is:
pan
'cooked in this?' is the definition.
(cooking vessel)
'prawns occasionally' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternate letters of 'prawns' are 'PAN'.
(Other definitions for pan that I've seen before include "all in many words, initially" , "'Mythical god, half man, half goat (3)'" , "Severely criticise; god" , "Shallow vessel" , "Pot" .)