Using a box grater or a food processor, shred cauliflower into crumbles. Reserve 4 cups; store the remainder in the fridge or freezer for future pizzas.
Cook cauliflower in microwave in a large microwave-safe bowl for 8 minutes. Allow to cool 10 minutes.
Add eggs, 2 cups shredded mozzarella cheese, oregano, basil and garlic powder and stir to combine. Preheat oven to 450°F.
Lightly grease 2 baking sheets (or pizza pans); divide mixture into 12 balls. Place balls on sheets and pat each into a thin round about 4 inches wide. Bake in oven 15 minutes until golden brown (the edges might be charred; this is OK).
Remove sheets from oven and heat broiler. Top each mini crust with pizza sauce, basil leaves, remaining mozzarella and Parmesan cheeses and tomato slices.
Broil pizzas until cheese is melted and tomatoes are slightly roasted, about 5 minutes. Remove from oven and let cool 5 minutes before serving.