Preheat oven to 425°F. If you have a pizza stone, place it in the oven. If you don’t, have a pizza pan or other large baking pan at hand (but it doesn’t need to preheat).
In a food processor, add the polenta, rice, chickpea flour, garlic powder, and sea salt and pulse first to combine, then process just until the mixture comes together in a ball on the blade.
Remove the dough ball and place it on a large sheet of parchment paper. Cover with another piece of parchment. Roll out the dough with a rolling pin between the parchment sheets to about 12" diameter or more, and ½" thick.
Remove the top sheet of parchment from the dough. Using a pizza peel or a very large tray/plate, transfer the pizza crust to the pizza stone (with the single layer of parchment still underneath the dough).
Bake for 25 minutes, until it is golden around the edges and firm in the center. Remove the pizza stone to let the crust cool slightly for few minutes while preparing the toppings.
When ready to bake, increase oven temperature to 450°F. Using a large plate or your pizza peel, remove the crust from the pizza stone/ pan and invert to remove the parchment.
Sprinkle the cornmeal over stone/pan, and place on pizza. Add toppings (see suggestions), and bake for 13 to 15 minutes, until heated through, and longer if desired for crispier edges/crust. Remove, let sit for 3 to 5 minutes, then serve.