Preheat the oven to 400 degrees F (200 degrees C). Grease a 10x13-inch baking dish.

Place shredded zucchini in a colander and sprinkle salt on top. Press down to drain as much water as possible. Let sit for 10 minutes. Transfer to a large bowl.

Add eggs, 1/2 of the mozzarella cheese, Parmesan cheese, Italian seasoning, and garlic powder to the zucchini. Mix well. Press mixture into the prepared baking dish.

Bake uncovered in the preheated oven for 20 minutes.

Heat a large skillet over medium-high heat. Cook and stir ground beef and onion in the hot skillet until beef is browned and crumbly, 5 to 7 minutes. Drain and discard grease. Mix pizza sauce with cooked beef and spoon over zucchini mixture in the baking pan.

Sprinkle remaining mozzarella cheese over the meat. Top with pepperoni slices.

Return baking dish to the hot oven and bake until mozzarella cheese is melted, 15 to 20 minutes more.