Check out return of fungus within this month (7)
I believe the answer is:
inspect
'check out' is the definition.
(thesaurus)
'return of fungus within this month' is the wordplay.
'return of' shows that the letters should be reversed in order.
'fungus' becomes 'cep' (Boletus edulis - an edible mushroom).
'within' is an insertion indicator.
'this month' becomes 'inst' (I've seen this before).
'cep' in reverse letter order is 'pec'.
'pec' put inside 'inst' is 'INSPECT'.
(Other definitions for inspect that I've seen before include "Scan" , "Carefully examine" , "Go over" , "Scrutinise" , "Examine officially" .)