What's in the oven is only meat (7)
I believe the answer is:
venison
'meat' is the definition.
(venison is a kind of meat)
'what's in the oven is only' is the wordplay.
'what's in' says the answer is hidden in the clue.
'VENISON' is hidden in the letters of 'oven is only'.
(Other definitions for venison that I've seen before include "Deer (as food)" , "Type of meat" , "Meat - in ovens (anag)" , "Deer meat" , "Flesh of deer" .)