Bother to put on duck sauce (5)
I believe the answer is:
pesto
'sauce' is the definition.
(I've seen this before)
'bother to put on duck' is the wordplay.
'bother' becomes 'pest'.
'to put on' means one lot of letters go next to another.
'duck' becomes 'o'.
'pest'+'o'='PESTO'
(Other definitions for pesto that I've seen before include "Green sauce" , "Italian sauce containing basil" , "Saucy work" , "Basil and pine nut sauce" , "Pasta sauce variety" .)