Stir yeast, flaxseed meal, and sugar into 2 cups warm water. Let stand 10 minutes, or until liquid is cloudy.
Meanwhile, whisk together tapioca starch, rice flours, xanthan gum, and salt in large bowl.
Stir yeast mixture into flour mixture until soft dough begins to form, then stir in oil.
Coat two 13-inch round pizza pans or one 18- x 13-inch baking sheet with oil. Divide dough between round pans or scoop into baking sheet, and coat hands with oil. Gently press and shape dough by hand to fit prepared pan(s). The dough will shrink as it bakes, so be sure to spread all the way to the edges of the pan.
Set dough aside in warm place to rise 1 1/2 hours. (You won’t see much, but the yeast will be working.).
Preheat oven to 425°F Par-bake pizza crusts 15 to 20 minutes, or until just golden brown. At this point, you can keep the par-baked crusts in the fridge for up to two days, or freeze for up to three months.
Add preferred toppings, return to oven, and bake 5 to 7 minutes more, or until cheeses begin to melt and/or toppings brown. Because of the short baking time, you should use toppings that do not require cooking - no raw sausage, for example. Fresh mozzarella, thinly sliced soft veggies, fresh herbs, etc. would be great.