Position an inverted baking sheet in the lower third of the oven and preheat to 450 degrees . Toss 2 pounds grated zucchini with 3/4 teaspoon salt in a colander. Let stand for 20 minutes, then squeeze dry. In a large skillet, cook the zucchini and 1 finely chopped onion in 1 tablespoon extra- virgin olive oil until softened, about 7 minutes; transfer to a large bowl, season with pepper and freeze for 15 minutes. Stir in 1/2 cup each grated parmigiano-reggiano cheese and grated asiago cheese. Divide 1 pound prepared pizza dough in half. On a parchment-lined rimless or inverted baking sheet, stretch out 1 piece of dough to a 12-inch round; brush with 1 tablespoon extra-virgin olive oil. Sprinkle half of the zucchini mixture on top, leaving a 1/2-inch border, and slide onto the hot baking sheet. Bake until golden-brown, 12 to 15 minutes. Repeat with the remaining ingredients to make a second pizza.