Tex-Mex food -- it will be eaten by donkey (7)
I believe the answer is:
burrito
'tex-mex food' is the definition.
(burrito is a Mexican dish)
'it will be eaten by donkey' is the wordplay.
'will be eaten by' is an insertion indicator.
'donkey' becomes 'burro' (term for a small donkey).
'it' going inside 'burro' is 'BURRITO'.
(Other definitions for burrito that I've seen before include "Mexican food" , "dish from Mexico" , "Tortilla folded round a filling" , "Mexican dish - rub trio (anag)" , "Mexican dish of tortilla folded around a filling" .)