Gents cooked outside food and I start eating with gusto (3,5,2)
I believe the answer is:
get stuck in
'start eating with gusto' is the definition.
'gents cooked outside food and i' is the wordplay.
I cannot quite understand how this works, but
'food' could be 'tuck' (I've seen this before) and 'tuck' is found within the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is found in the answer.
'i' is within the answer.
The remaining letters 'gets' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
(Another definition for get stuck in that I've seen is " Concentrate on your work!".)