Cut the cauliflower into florets. Place the florets on a baking sheet, drizzle with the oil and sprinkle with 1/2 teaspoon salt. Toss the florets to coat evenly and roast, stirring halfway through for even cooking, until very tender with brown and crispy edges, about 45 minutes. Let cool for 15 minutes.
Transfer half the florets to the center of a large clean dish towel. Wrap up all sides of the towel and twist it up to squeeze out the excess moisture. Squeezing out the moisture is very important because it will help prevent the crust from falling apart. Transfer the florets to a food processor and pulse until you get a rice-like texture. Repeat with the remaining florets.
Line a baking sheet or pizza pan with parchment. Generously spray the parchment with cooking spray. Do not skip this step.
In a large bowl, add the pulsed cauliflower, egg, goat cheese, oregano, turmeric, 1/2 teaspoon salt and 1/2 teaspoon pepper. Use your hands and mix well. Press the dough out into a 9-inch circle about 1/3-inch thick on the prepared baking sheet. Bake until the crust is golden brown and the edges are crispy, 25 to 30 minutes.
Spread the marinara sauce over the crust, leaving a 1-inch border around the edge. Add the cooked sausage, then sprinkle with the mozzarella. Return to the oven until the cheese melts, another 10 minutes. Let sit for 5 minutes, then top with basil leaves and serve.