Morsel on red dish (7)
I believe the answer is:
rarebit
'dish' is the definition.
(rarebit is a kind of dish)
'morsel on red' is the wordplay.
'morsel' becomes 'bit' (synonyms).
'on' says to put letters next to each other.
'red' becomes 'rare' (as in a rare steak).
'bit' after 'rare' is 'RAREBIT'.
(Other definitions for rarebit that I've seen before include "Welsh food?" , "Welsh snack" , "Cheese on toast - arbiter (anag)" , "Arbiter (anag) -- snack" , "Arbiter of traditional Welsh dish" .)