Tortilla chip hidden in tuna chowder (5)
I believe the answer is:
nacho
'tortilla chip' is the definition.
(nacho is a kind of tortilla chip)
'hidden in tuna chowder' is the wordplay.
'hidden in' indicates the answer is hidden within the clue.
'NACHO' can be found hidden inside 'tuna chowder'.
(Other definitions for nacho that I've seen before include "chip production line unit" , "Nibble" , "Piece of tortilla served with sauce" , "Tortilla chip topped with cheese and spices" , "Tortilla with cheese, etc" .)