American tucked into his unusual Japanese food (5)
I believe the answer is:
sushi
'japanese food' is the definition.
(sushi is a type of Japanese food)
'american tucked into his unusual' is the wordplay.
'american' becomes 'US' (United States).
'tucked into' indicates putting letters inside.
'unusual' indicates an anagram.
'his' anagrammed gives 'shi'.
'us' put into 'shi' is 'SUSHI'.
(Other definitions for sushi that I've seen before include "rice dishes" , "Japanese cold rice dish" , "exotic dish" , "Asian food" , "Asian dish" .)