Preheat oven to 425º and grease a cast-iron skillet with cooking spray. In a large bowl, combine cauliflower, 1 cup mozzarella, eggs, 1/2 cup Parmesan, and garlic powder and season with salt and pepper.
Press mixture into skillet, making sure to get up the sides, and bake until deeply golden and dry, 25 minutes.
Spoon a thin layer of pizza sauce over crust and sprinkle with remaining mozzarella and Parmesan. Top with mini pepperoni and bake 5 minutes more.
Sprinkle with basil, slice, and serve.