In Tijuana, chosen fast food (5)
I believe the answer is:
nacho
'food' is the definition.
(nacho is a kind of food)
'in tijuana chosen fast' is the wordplay.
'in' says the answer is hidden in the clue.
'NACHO' is hidden within 'tijuana chosen fast'.
(Other definitions for nacho that I've seen before include "part of a snack?" , "kind of chip" , "Tortilla with cheese, etc" , "Hot snack" , "Nibble" .)