Preheat your oven to 400°F (200°C).

Grate the zucchini and sprinkle with salt. Let it rest for about 10 minutes.

Drain the zucchini using a clean kitchen towel to remove excess liquid.

Mix the drained zucchini with eggs, Parmesan cheese, and half of the mozzarella cheese.

Grease a 9x13-inch baking dish and spread the zucchini mixture to form the crust. Bake for 20 minutes.

Cook ground beef and chopped onion in a skillet until browned and translucent, about 6-8 minutes.

Add the pizza sauce, bell pepper, mushrooms, oregano, garlic powder, and black pepper to the meat mixture. Stir and simmer for 5 minutes.

Spread the beef mixture evenly over the baked crust.

Sprinkle the remaining mozzarella and cheddar cheese over the beef layer.

Bake the assembled casserole for an additional 20 minutes until the cheese is melted and bubbly.

Let cool for a few minutes before serving.