Feast on duck with a vegetable (5)
I believe the answer is:
beano
'feast' is the definition.
(I've seen this before)
'duck with a vegetable' is the wordplay.
'duck' becomes 'o' (resembles zero - 'duck' in cricket).
'with' means one lot of letters go next to another.
'a vegetable' becomes 'bean' (bean is a kind of vegetable).
'o' put after 'bean' is 'BEANO'.
'on' acts as a link.
(Other definitions for beano that I've seen before include "Junket - children's comic" , "Kids' comic" , "Rowdy jollification" , "Informal party" , "Function" .)