Preheat oven to 400°F.
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.
In a large skillet over medium heat, add the chopped cauliflower and 3 tablespoons water. Bring to a simmer and cook, stirring occasionally, until the cauliflower "rice" is soft and tender (about 5–8 minutes). Add more water only if it begins to stick.
Transfer the cooked cauliflower to a fine-mesh sieve or colander and let drain briefly, then spread the cauliflower onto a thin kitchen towel or cheesecloth. When cool enough to handle, tightly gather the cloth and squeeze out as much liquid as possible until the cauliflower is noticeably drier.
Return the drained cauliflower to a mixing bowl. Add 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. Mix until evenly combined.
Line a pizza pan or baking sheet with parchment paper. Spread the cauliflower mixture on the parchment and shape into a circle about 1/2 inch thick.
Bake the crust for 30 minutes, until it is set and beginning to brown.
Remove the crust from the oven. Spread 1/2 cup pizza sauce evenly over the crust. Top the sauce with 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 sauce is heated through and the toppings are warmed and slightly softened, about 8–10 minutes.
Let the pizza rest for a few minutes before slicing and serving.