Preheat your oven to 400°F (200°C).

Toss the shredded zucchini with a pinch of salt and let it sit for about 10 minutes.

Squeeze out as much moisture from the zucchini as you can using a clean kitchen cloth or paper towels.

In a large mixing bowl, combine the drained zucchini with eggs, grated Parmesan cheese, and half of the mozzarella.

Grease a 9x13-inch baking dish and press the zucchini mixture evenly into the bottom.

Bake the crust for 20 minutes, or until set and lightly browned.

While the crust is baking, heat a skillet over medium-high heat. Add the ground beef and chopped onions, and cook until browned.

Add the pizza sauce, diced bell peppers, sliced mushrooms, dried oregano, garlic powder, and black pepper to the skillet, and simmer for about 5 minutes.

Spread the beef mixture evenly over the baked crust.

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

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

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