Bother with duck sauce (5)
I believe the answer is:
pesto
'sauce' is the definition.
(I've seen this before)
'bother with duck' is the wordplay.
'bother' becomes 'pest'.
'with' 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 "Basil and pine nut sauce" , "Pasta sauce based on basil" , "Basic sauce" , "Sauce of basil, pine nuts and garlic" , "Ligurian food" .)