Gusto shown over half of cheese roll (7)
I believe the answer is:
brioche
'roll' is the definition.
(I know that brioche is a type of roll)
'gusto shown over half of cheese' is the wordplay.
'gusto' becomes 'brio' (I've seen this in another clue).
'shown over' is a charade indicator (letters next to each other) (in a down clue, some letters go above others).
'half of' indicates taking half.
'cheese' halved is 'che'.
'brio'+'che'='BRIOCHE'
(Other definitions for brioche that I've seen before include "French cake-like bread" , "Small French roll" , "Soft roll sometimes mixed with currants" , "Sweet french roll" , "Bread roll of Normandy" .)