Celebration justifies tasty sandwiches (6)
I believe the answer is:
fiesta
'celebration' is the definition.
(fiesta is a kind of celebration)
'justifies tasty sandwiches' is the wordplay.
'sandwiches' indicates a hidden word (the answer is sandwiched in by the clue).
'FIESTA' is hidden within 'justifies tasty'.
(Other definitions for fiesta that I've seen before include "celebration abroad" , "(Spanish) religious festival" , "Public celebration in Spain" , "Spanish holiday" , "Elaborate public party, in Spain perhaps" .)