Where one could select a banana without thinking about it (3,2,4)
I believe the answer is:
out of hand
'without thinking about it' is the definition.
(as in dismissing something out of hand)
'where one could select a banana' is the wordplay.
I cannot really understand how this works, but
'one' could be 'o' (I've seen this in other clues) and 'o' is present in the answer.
'a' could be 'an' and 'an' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
(Other definitions for out of hand that I've seen before include "Cards might be taken thus" , "How card may be played" , "Banana so" , "peremptorily selected?" , "Beyond control" .)