Reheat in a microwave (3)
I believe the answer is:
zap
'reheat in a microwave' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for zap that I've seen before include "Kill or shoot (in a microwave oven?)" , "Attack" , "Keep changing TV channels" , "Destroy, obliterate" , "Hit (colloq.)" .)