Preheat oven to 400°F (200°C).
Remove the core from the cauliflower and cut into small florets.
Place the florets in a food processor and pulse until the cauliflower resembles rice.
Transfer the cauliflower "rice" to a large skillet, add the 3 tablespoons water, and cook over medium heat, stirring occasionally, until the cauliflower is soft and most of the moisture has evaporated (about 5–8 minutes).
Drain the cooked cauliflower in a fine-mesh strainer, then spread it onto a thin kitchen towel or cheesecloth. Let it cool until it is safe to handle, then gather the towel and squeeze firmly to remove as much liquid as possible.
Transfer the drained cauliflower to a bowl. Add the 2 egg whites, 1 cup shredded low-fat mozzarella, 1/4 teaspoon garlic powder, 1/4 teaspoon dried oregano, 1/4 teaspoon dried basil, 1/4 teaspoon onion powder, and 1/4 teaspoon smoked paprika. Stir until well combined. If the mixture still seems very wet, return it to the towel and squeeze out any remaining moisture.
Line a pizza pan with parchment paper. Spread the cauliflower mixture onto the parchment and shape it into a circle about 1/2 inch thick, pressing the edges to form a crust.
Bake the crust in the preheated oven for 30 minutes, or until it is set and lightly golden.
Remove the crust from the oven and spread the 1/2 cup pizza sauce (no sugar added) evenly over it. Top with the 2 tablespoons diced green pepper, 2 tablespoons diced mushrooms, 2 tablespoons diced red onion, and 2 tablespoons sliced black olives.
Return the pizza to the oven and bake until the toppings are heated through and the sauce is hot, about 8–10 minutes.
Allow the pizza to rest for a few minutes before slicing and serving.