Turn chopped fungi over for observer (9)
I believe the answer is:
spectator
'for observer' is the definition.
(spectator is a kind of observer)
I don't understand how the rest of the clue works.
(Other definitions for spectator that I've seen before include "Onlooker at game" , "fan" , "One watching a game" , "Looker-on" , "Cat poster (anag.)" .)