Preheat oven to 400°F (200°C) and grease a 24-cup mini muffin tin thoroughly with non-stick spray.
Steam the riced cauliflower for 5 minutes or microwave in a covered bowl until tender, then allow to cool slightly.
Place cooked cauliflower in a clean kitchen towel and squeeze vigorously to remove all excess moisture; this step is critical for a firm crust.
In a large mixing bowl, combine the dry cauliflower pulp, beaten egg, 1/2 cup mozzarella, parmesan, oregano, garlic powder, and salt.
Distribute the mixture evenly into the muffin tin cups, pressing down firmly with a spoon to compact the base.
Bake for 15 to 18 minutes or until the edges are golden brown and the crusts feel set.
Remove from the oven and top each bite with 1/2 teaspoon of pizza sauce, a sprinkle of mozzarella, and one mini pepperoni slice.
Return to the oven and bake for an additional 5 to 7 minutes until the cheese is melted and bubbling.
Let the bites cool in the pan for 5 minutes before using a small offset spatula or knife to gently lift them out.