The most common and most likely answer to this crossword clue is the 9 letter word BEANFEAST
I've seen this crossword clue in Financial Times
B
E
A
N
F
E
A
S
T
Buddy explains!
The straight part
We know that "Annual dinner to appeal most to vegans" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case annual dinner to appeal most to vegans = beanfeast.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 BEANFEAST mean?
BEANFEAST noun- A dinner party given to the employees of a firm.
- Any similar social occasion.