... hot dish is cold, it's said (6)
I believe the answer is:
chilli
'hot dish' is the definition.
(I've seen this before)
'cold it's said' is the wordplay.
'cold' becomes 'chilly' (I've seen this before).
'it's said' indicates a 'sounds like' (homophone) clue.
'chilly' sounds like 'CHILLI'.
'is' acts as a link.
(Other definitions for chilli that I've seen before include "Spicy seed pod" , "or not on the radio" , "Small hot pod" , "Burner" , "Small hot-tasting pod" .)