Preheat your oven to 400°F (200°C).

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.

In the same bowl, mix the drained zucchini, eggs, Parmesan cheese, and half of the mozzarella cheese. Mix well to form the crust mixture.

Grease a 9×13-inch baking dish. Press the zucchini mixture evenly into the bottom of the dish to form the crust.

Bake the crust in the preheated oven for 20 minutes, or until it is set and lightly browned.

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. 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.

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

Sprinkle the remaining mozzarella cheese and all of the cheddar cheese over the top.

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

Remove from the oven and let the casserole cool for a few minutes before slicing and serving.