Crunchy sandwich (4)
I believe the answer is:
taco
'crunchy sandwich' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for taco that I've seen before include "Mexican rolled pancake with a filling" , "Filled tortilla roll" , "Tortilla rolled round a filling" , "Set of three" , "Coat with Mexican dish" .)