Files moved behind bananas, say, as annoyance to greengrocer (5-5)

'as annoyance to greengrocer' is the definition.
I know nothing about this answer so I can't tell whether it can be defined by this definition.

'files moved behind bananas' is the wordplay.
'moved' indicates anagramming the letters.
'behind' is a charade indicator (letters next to each other).
'bananas' becomes 'fruit' (I can't explain this - if you can you should believe this answer much more).
'files' anagrammed gives 'flies'.
'flies' put after 'fruit' is 'FRUIT-FLIES'.

'say' acts as a link.

Can you help me to learn more?