Nonsense written about a small Sunday meal (5)
I believe the answer is:
roast
'sunday meal' is the definition.
(I've seen this before)
'nonsense written about a small' is the wordplay.
'nonsense' becomes 'rot' (I've seen this before).
'written about' indicates putting letters inside.
'small' becomes 's' (abbreviation - e.g. clothes size).
'a'+'s'='as'
'rot' placed around 'as' is 'ROAST'.
(Other definitions for roast that I've seen before include "Pull to pieces" , "Oven-cooked joint" , "Large piece of oven-cooked meat" , "Berate - cook" , "Oven joint" .)