The most common and most likely answer to this crossword clue is the 4 plus 3 plus 3 letter word GOOD FOR YOU
I've seen this crossword clue in Financial Times
G
O
O
D
F
O
R
Y
O
U
Buddy explains!
The straight part
We know that "Veggies are meant to be this/well done" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case veggies are meant to be this/well done = good for you.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.