Preheat oven to 425°F (190°C)

Line a large baking sheet with parchment paper and lightly coat paper with cooking spray.

In a food processor, add the chopped cauliflower and pulse until pieces are about the size of a grain of rice.

Place the processed cauliflower in a microwave-safe dish, cover with plastic wrap, and microwave on high for 8 minutes.

When cool enough to handle, place cauliflower in a cheesecloth or towel and squeeze to remove moisture.

Add egg and egg white to a medium-sized bowl and beat until fully mixed. Then add the cauliflower and 1/2 cup of the mozzarella and combine until ingredients resemble a dough.

Spread dough mixture on sprayed parchment-lined baking sheet in a quarter-inch thick layer (in desired shape) and bake.

Once the crust is firm to the touch and has started to brown, about 15 minutes, remove from oven and spread the sauce on the crust, then sprinkle with cheese, mushrooms, onions, and spinach.

Return the assembled pizza to the oven and bake until cheese is melted and golden brown, about 5-6 minutes.

Let cool slightly before serving.