Preheat the oven to 400 degrees F (200 degrees C). Grease a 9x13-inch baking dish.

Place zucchini into a colander and sprinkle with salt; let drain for 15 minutes, then squeeze out the moisture.

Combine zucchini, 1 cup mozzarella, and 1/2 cup Monterey Jack in a large bowl. Mix in Parmesan and eggs until well combined. Press into the prepared baking dish.

Bake, uncovered, in the preheated oven for 20 minutes.

Meanwhile, heat a large skillet over medium-high heat. Add ground beef and onion to the hot skillet; cook and stir until beef is crumbly, evenly browned, and no longer pink. Drain and discard any excess grease. Stir in tomato sauce and Italian seasoning.

Remove crust from the oven and spoon sauce mixture over top. Scatter bell pepper, mushrooms, black olives, and remaining mozzarella and Monterey Jack over sauce.

Return to the oven and bake until heated through, about 20 minutes. Let sit for 5 minutes before slicing into six pieces and serving.