Bananas some left in a wheat-based dish (8)
I believe the answer is:
semolina
'wheat-based dish' is the definition.
(dish using wheat)
'bananas some left in a' is the wordplay.
'bananas' indicates anagramming the letters (informal term for mad).
'left' becomes 'l' (common abbreviation).
'some' anagrammed gives 'semo'.
'semo'+'l'+'in'+'a'='SEMOLINA'
(Other definitions for semolina that I've seen before include "dessert" , "sweet" , "What could be for pudding" , "Wheat product used in pasta" , "Pudding flour" .)