There are only so many ways to prepare that.
I'm trying to think what it would take to cook an all-rice pizza. Rice bread is easy enough for the crust. There's probably some way to process rice milk into cheese. We could even construct a box for it from layer upon layer of rice paper. But, when we get to the pizza sauce, I'm completely stumped.
Of course, that wouldn't actually give him the nutrients he'll need to live. So, this may constitute a deeper problem.