Insist on piece of chicken for celebration (7)
I believe the answer is:
enforce
'insist on' is the definition.
(I've seen this before)
'piece of chicken for celebration' is the wordplay.
'piece of' says the answer is hidden in the clue.
'ENFORCE' is hidden in the letters of 'chicken for celebration'.
(Other definitions for enforce that I've seen before include "Impose with power" , "Apply law" , "Compel compliance or obedience" , "Administer with pressure (70" , "Compel or impose obedience, say to law" .)