Preheat oven to 420. Line with a piece of aluminum foil and spray with cooking spray.
Chop the stems off of the cauliflower and discard (or save for another recipe.) Roughly chop the remaining florets. Place florets in a food processor and pulse until you have a finely chopped cauliflower "snow". (You should have 2-3 cups of the "snow".)
Place cauliflower "snow" in a microwave safe bowl and microwave on high for 4 minutes. Pour the cauliflower out on a tea towel (or on paper towels) and allow to cool for a couple of minutes. Use the tea towel to wring out the excess water from the cauliflower. (Alternatively, you can use paper towels to grab a handful of cauliflower at a time and squeeze out the excess water.) You want to get all possible moisture out of the cauliflower or it will crumble when baked. Your cauliflower will now resemble a pulp-like substance.
Add the cauliflower "pulp" to a large bowl. Add egg, salt, parmesan cheese, mozzarella cheese, Italian seasoning, and garlic powder to the bowl and mix with your hands until all ingredients are incorporated. Shape it into a ball, then place the ball in the center of your prepared baking sheet.
Roll out into a circle. Transfer the crust on the foil only to the oven. (Not the pan, just place the foil or right on the oven rack). Bake for 10-15 minutes until golden. Remove from oven and return the crust and foil to the baking sheet. Spread pizza sauce on top.
Sprinkle with cheese (and any other desired toppings) and return to oven (on the baking sheet) for another 10-15 minutes until cheese is melty. Serve warm and top with fresh parsley or basil if desired.