Say how awful the ham is when you cook it (5)
I believe the answer is:
roast
'it' is the definition.
The definition suggests a singular noun which matches the answer.
'say how awful the ham is when you cook' is the wordplay.
I cannot really understand how this works, but
'when' could be 'as' and 'as' is found within the answer.
The remaining letters 'rot' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for roast that I've seen before include "Traditional Sunday lunch" , "The Sunday -----, with all the trimmings!" , "Give a telling off to - cook" , "Oven-cooked joint" , "Cooked like chestnuts tonight" .)