Top green veg, diced for a dish best served cold (7)
I believe the answer is:
revenge
'a dish best served cold' is the definition.
(I've seen this in another clue)
'top green veg diced' is the wordplay.
'top' means to remove the first letter.
'diced' indicates an anagram.
'green'+'veg'='greenveg'
'greenveg' with its first letter taken off is 'reenveg'.
'reenveg' is an anagram of 'REVENGE'.
'for' is the link.
(Other definitions for revenge that I've seen before include "Malicious retaliation" , "An eye for an eye" , "Satisfaction taken for injury" , "Retribution" , "Ship remembered in verse" .)