He's very handsome! It's hard to tell from just a pic though if he's overweight. Are you able to weigh him on a scale? Zons are one of the species prone to being perch potatoes and gaining lots of weight. Does he let you touch him? Can you feel his keel bone or is it padded in fat?
I'm not sure if he has other perches in the cage that we can't see but if he only has what look like dowels(but perhaps its a different type of straight natural wood) I'd like to respectfully mention that they can cause sores from being so smooth and rounded so its good to have a wide variety of different types and sizes of natural perches so he can exercise his feet and be more able to grip different textures and sizes like he would flying in the wild.
I know some folks still use dowels to be able to have a perch that spans the whole cage but they will wrap it in vet wrap to make it softer and better on their feet.
I'd be careful of that toy next to him as well with all the dangling chain. Birds are unfortunately so prone to getting into mischief with even the safest of toys.
I hope this didn't come off as rude or judging that's absolutely not my intent at all especially since you just asked about his weight.
If you have other perches then please disregard that part of the post. Like folks always say you can't see it all from just a single picture so you never know what the rest of the cage looks like
