Sampled in bistro — a stonking Sunday dinner (5)
I believe the answer is:
roast
'sunday dinner' is the definition.
(a roast dinner is often eaten on Sunday)
'sampled in bistro a stonking' is the wordplay.
'sampled' says the answer is hidden in the clue (I've seen 'sample' mean this (I've seen this in other clues)).
'ROAST' can be found hidden inside 'in bistro a stonking'.
(Other definitions for roast that I've seen before include "Oven joint" , "Trash" , "Oven-cook, tease" , "Carpet" , "Meat to get hot" .)