Panthers don't eat fruits/veggies as much as veileds, but I would try anywhere from mustard greens, butternut squash, a bit of mango here and there as a treat, maybe some kale, or strawberries all the way to apple slices (thin thin thin) or anything else that is safe.
Look up SandraChameleon's gutload blog. A lot of those gutloads are also safe to feed the cham.