Bistro boss’s resistance to trust EU area bananas (12)
I believe the answer is:
restaurateur
'bistro boss's' is the definition.
'resistance to trust eu area bananas' is the wordplay.
'resistance' becomes 'r' (electronics abbreviation).
'to' is a charade indicator (letters next to each other).
'bananas' is an anagram indicator (informal term for mad).
'trust'+'eu'+'area'='trusteuarea'
'trusteuarea' is an anagram of 'estaurateur'.
'r'+'estaurateur'='RESTAURATEUR'
(Other definitions for restaurateur that I've seen before include "like Oliver?" , "Proprietor of an eating establishment" , "One catering to diners" , "I supply meals" , "Person running eating house" .)