The most common and most likely answer to this crossword clue is the 8 letter word TERIYAKI
I've seen this crossword clue in The Guardian
T
E
R
I
Y
A
K
I
More clues leading to the result TERIYAKI
Buddy explains!

The straight part
We know that "Japanese dish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case japanese dish = teriyaki.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TERIYAKI mean?
TERIYAKI noun- A cooking technique used in Japanese cuisine in which foods are broiled or grilled in a sweet soy sauce marinade.
- A sweet soy sauce marinade