Group desire to leave courgette stewing (5)
I believe the answer is:
octet
'group' is the definition.
(group of eight musicians)
'desire to leave courgette stewing' is the wordplay.
'desire' becomes 'urge' (I've seen this in another clue).
'to leave' is a deletion indicator.
'stewing' indicates anagramming the letters.
'courgette' with 'urge' taken away is 'cotte'.
'cotte' is an anagram of 'OCTET'.
(Other definitions for octet that I've seen before include "A group of eight, may be singers" , "Mendelssohn wrote this" , "Piece for eight players" , "A number of musicians" , "Played" .)