Put on goose at last -- must be cooked! (4)
I believe the answer is:
done
'cooked' is the definition.
('done' can be similar in meaning to 'cooked')
'put on goose at last' is the wordplay.
'put on' becomes 'don' ('don' can be a synonym of 'put on'**).
'at last' indicates one should take the final letters.
The last letter of 'goose' is 'e'.
'don'+'e'='DONE'
'must be' is the link.
(Other definitions for done that I've seen before include "agreed" , "Completed" , "Thoroughly cooked; accomplished" , "Finished or ended" , "Cooked; carried out" .)