I give my chams kale to eat as a treat. I have been looking around and can't find where other lettuces (veggies or fruits) it is safe to give them. I am trying to keep them from decimating their hibiscuses.
Okay.
No tomato, brocolli, spinach or any other vegetable with high oxalates!
The preferred green to offer veileds here is collard.
In fact that is all I offer them, besides the plants in the enclosures.
It (like most dark leafy greens) is very high in calcium.
Veileds are really the only commonly kept species that you want to offer vegetation to and some of them won't ever touch it.
If your chameleons don't want to eat it don't worry.
You can clip a piece on the side of the cage. If you have fake plants, he is probably not going to notice it or even bother with it. They often eat hibiscus flowers too.