what ever your bird likes best is a treat, i give nutri berries, grapes, cherries etc as treats even the occassional tiny nibble of a cookie (very rarely) pasta, noodles and seeded bread
nut is currently having a hissy fit over the food bowl as its only got pellets in it, the good stuff does not go in till i have to go to work, when i place nutri berries in her toys etc
I have an african red belly about same size as your bird and a mealy amazon that we give bananna chips to as treats and they love them and so do i cause you can get them at the dollar store really cheap. The birds also like to crunch on stuff and since they are dried out the chip crunches when they eat it. Also apple ones are good too if your bird likes it and both are all natural nothing added just dried chips.