Agent sat preparing dinner? (6)
I believe the answer is:
repast
'dinner?' is the definition.
(dinner is a kind of repast)
'agent sat preparing' is the wordplay.
'agent' becomes 'rep' (short for representative).
'preparing' indicates anagramming the letters (the same letters prepared differently).
'sat' with letters rearranged gives 'ast'.
'rep'+'ast'='REPAST'
(Other definitions for repast that I've seen before include "Food - tapers (anag)" , "Banquet" , "Prates about meal" , "lunch?" , "A meal concerning time gone by" .)