The most common and most likely answer to this crossword clue is the 4 plus 3 plus 4 letter word SURF āNā TURF
I've seen this crossword clue in Independent
S
U
R
F
ā
N
ā
T
U
R
F
Buddy explains!
The straight part
We know that "mixed dish" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mixed dish = surf ānā turf.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.