Place quinoa in a bowl and cover with 1 inch of water. Let soak for at least 8 hours, or overnight.
Drain quinoa. Place in a blender, small food processor (a bullet blender works perfectly) and blend with water, baking powder, and salt until smooth, about 2 minutes.
Line a 9-inch cake pan with parchment and oil the bottom and the sides well. Pour the batter into the pan and smooth it out to the edges.
Bake at 425F for 15 minutes. Using a spatula, carefully flip the crust and bake for another 5. The crust will shrink as it bakes. Top with favorite toppings, and bake for another 5-10 minutes, until toppings are heated through.