Preheat oven to 425°. Line a baking sheet with parchment paper.
Grate the cauliflower or use a food processor until you have 2 cups of cauliflower crumbles. Place in a bowl and microwave for 8 minutes until soft. Let cool. Using a clean dish towel or cheese cloth, drain cauliflower completely, removing as much water as possible and place back in the bowl.
Mix in the egg, 1 cup mozzarella, Parmesan cheese, salt and pepper. Form into a 10-inch round disk on the sheet pan lined with parchment. Bake for 10-15 minutes, until golden brown.
Top the pizza with the sauce, remaining mozzarella, turkey pepperoni and red pepper flakes. Bake in the oven another 10 minutes until cheese is melted and bubbly. Slice and serve.