Grate zucchini and measure out 4 cups. Sprinkle salt over zucchini and let sit for 10 minutes. Ring out zucchini to remove any excess water and mix together with pepper, eggs, 1 cup mozzarella cheese, 1 cup cheddar cheese and parmesan cheese. Stir to combine and spread evenly into prepared baking dish. Bake 20 minutes. Remove from oven and top with pizza sauce, remaining cheeses and any desired pizza toppings. Bake 15 more minutes and remove. Cool 5 minutes before cutting and serving.