What's in the oven is only meat (7)
I believe the answer is:
venison
'meat' is the definition.
(I know that venison is a game meat)
'what's in the oven is only' is the wordplay.
'what's in' indicates the answer is hidden within 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" .)