Preheat oven to 425°F.

Line two large baking sheets with parchment paper. Set aside.

Thaw the bags of frozen riced cauliflower in the microwave according to package directions. Set a large fine-meshed sieve over the sink. Turn the riced cauliflower into the sieve and strain.

Place the cauliflower on the center of a large dish towel. Gather the towel into a sack and hold over a bowl or sink. Firmly squeeze the cauliflower until water no longer drips out.

Transfer the cauliflower to a large mixing bowl. Press down on it with paper towels to remove any last traces of water. Add the garlic powder, salt, black pepper, egg, and cornstarch. Mix thoroughly with a fork until the cauliflower is evenly coated and pale yellow in color.

Divide the cauliflower into two equal mounds on each baking sheet. With clean hands, firmly pack the mounds into discs approximately 1/2 inch thick and 7-8 inches in diameter.

Bake the cauliflower crusts on middle rack of oven for 35 minutes.

When the crusts are firm, browned on the edges, and slightly golden on top, open the oven door and quickly brush the surface of each with a thin layer of egg white. Close the oven and continue baking the crusts for 4-5 minutes longer.

Remove the baking sheet from the oven. Spread a generous 2 tablespoons of pizza sauce evenly onto the center of each cauliflower crust, leaving a 1/2-inch border around the sauce. Sprinkle equal amounts of shredded cheese and Italian seasoning over each cauliflower crust.

Return the pizzas to oven and bake until the cheese is bubbly and golden, 10-11 minutes.

Check to see that pizzas are done. Remove from oven or add time as needed.

Allow pizzas to cool on baking sheet for 2-3 minutes. Sprinkle pizzas with red pepper flakes, if desired, then slice and serve.