The most common and most likely answer to this crossword clue is the 11 letter word FLAVOURSOME
I've seen this crossword clue in The Daily Telegraph
F
L
A
V
O
U
R
S
O
M
E
Buddy explains!

The straight part
We know that "full of zest" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case full of zest = flavoursome.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 FLAVOURSOME mean?
FLAVOURSOME adjective- Characterised or marked by flavor(s); flavorful.