Offer nothing but pellets and after a few days it should change its mind. Once its set on pellets try feeding pellets in the morning and prawn at night, and as soon as it starts turning its nose up at the pellets don't feed prawn for a few days. Thats what I do with my green and it eats like a pig, you can't spoil them, and IMO offering "treats" are a waste of time and will just help make the fish fussy.