Used teeth on lightly-cooked snack (7)
I believe the answer is:
rarebit
'snack' is the definition.
(I've seen this before)
'used teeth on lightly-cooked' is the wordplay.
'used teeth' becomes 'bit' (I can't explain this - if you can you should give a lot more credence to this answer).
'on' is a charade indicator (letters next to each other).
'lightly cooked' becomes 'rare' (as in a rare steak).
'bit' put after 'rare' is 'RAREBIT'.
Can you help me to learn more?
(Other definitions for rarebit that I've seen before include "Cheese/toast savoury" , "Arbiter (anag) -- snack" , "Welsh food?" , "See 8 Across" , "Melted cheese on hot toast" .)