Preheat your oven to 400°F (200°C). This higher temperature helps set the zucchini crust quickly. In a large bowl, combine the shredded zucchini and salt. Let it sit for 10 minutes to release excess moisture.

After 10 minutes, squeeze out as much moisture as possible from the zucchini using a clean kitchen towel or cheesecloth. You should remove at least half a cup of liquid. Really squeeze hard to ensure the crust isn't soggy.

In the same bowl, combine the drained zucchini, eggs, Parmesan cheese, and 1 cup of the mozzarella cheese. Mix well until the mixture holds together when pressed.

Grease a 9x13-inch baking dish. Press the zucchini mixture evenly into the bottom of the dish to form the crust, pressing firmly to compact it.

Bake the crust in the preheated oven for 20 minutes, or until the edges are golden brown and the center feels firm to the touch.

While the crust is baking, brown the ground beef with the chopped onion in a skillet over medium heat until the beef is no longer pink, about 7 to 8 minutes. Break up the meat as it cooks. Drain any excess fat.

Stir in the pizza sauce, green bell pepper, mushrooms, oregano, garlic powder, and black pepper. Cook for another 5 minutes, stirring occasionally to blend the flavors.

Once the crust is ready, spread the beef mixture evenly over the zucchini crust.

Sprinkle the remaining 1 cup of mozzarella cheese and all of the cheddar cheese over the top, covering the entire surface.

Return the casserole to the oven and bake for an additional 20 minutes, or until the cheese is melted, golden, and bubbling.

Remove from the oven and allow the casserole to rest for 10 minutes before slicing and serving. This helps it hold together better.