Some Zoroastrians cook (5)
I believe the answer is:
roast
'cook' is the definition.
(I know this)
'some zoroastrians' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ROAST' is hidden within 'zoroastrians'.
(Other definitions for roast that I've seen before include "Berate - cook" , "Sunday dinner" , "Cooked meat; criticise" , "Oven-cooked joint" , "Trash" .)