Responses to preparing nice roast (9)
I believe the answer is:
reactions
'responses' is the definition.
(I know this)
'preparing nice roast' is the wordplay.
'preparing' is an anagram indicator (the same letters prepared differently).
'nice'+'roast'='niceroast'
'niceroast' with letters rearranged gives 'REACTIONS'.
'to' is the link.
(Other definitions for reactions that I've seen before include "Newton's law of motion says all actions have them" , "Responses, chemical perhaps" , "Mental or physical responses" , "What you may get with chemicals" , "Takes" .)