Preheat oven to 400 degrees F (200 degrees C). Line a baking sheet with parchment paper.
Place cauliflower florets in a food processor; pulse until chopped into grains the size of rice.
Fill a large pot with about 1 inch of water; bring to a boil. Add cauliflower “rice”; cook until softened, 4 to 5 minutes. Drain in a fine sieve and cool until running water.
Pour cauliflower onto a clean dish towel; roll up and twist edges. Wring out as much water as possible.
Transfer cauliflower to a large bowl. Add egg, mozzarella cheese, oregano, and salt; mix well. Spread on the lined baking sheet to about 1/2-inch thickness.
Bake in the preheated oven until firm to the touch and light golden brown in color, about 35 minutes.
Wringing out the water is the secret to this crust! It is surprisingly bendable for a veggie crust – you can pick it up just like any other pizza crust. This could be adapted to calzone, breadsticks, etc.
I think fresh basil or even minced spinach would be excellent in this crust.