Preheat your oven to 400°F (200°C).

In a mixing bowl, combine shredded zucchini and salt. Let sit for 10 minutes to draw out moisture.

Squeeze out excess moisture from the zucchini with a clean towel. Mix with eggs, grated Parmesan, and half of the shredded mozzarella.

Grease a 9x13-inch baking dish and press the zucchini mixture to form a crust. Bake for 20 minutes until set and golden brown.

In a skillet, heat ground beef and chopped onion over medium heat until browned. Drain excess fat.

Add pizza sauce, green bell pepper, mushrooms, oregano, garlic powder, and black pepper to the skillet. Cook for 5 minutes.

Spread the beef mixture over the crust evenly. Press down gently.

Top with the remaining mozzarella and all cheddar cheese. Bake for another 20 minutes until cheese is melted and bubbly.

Let the casserole cool for a few minutes before slicing and serving warm.