Squash cooked itself (6)
I believe the answer is:
stifle
'squash' is the definition.
(thesaurus)
'cooked itself' is the wordplay.
'cooked' indicates anagramming the letters (letters cooked into a new form).
'itself' is an anagram of 'STIFLE'.
(Other definitions for stifle that I've seen before include "Silence" , "Repress, choke" , "Quash" , "Suppress or suffocate" , "Muffle, suppress" .)