Preheat oven to 375°F (190°C).
Place zucchini slices on paper towels, sprinkle with salt, and let sit for 15 minutes to draw out moisture. Pat thoroughly dry with additional paper towels.
In a large skillet over medium heat, brown the ground beef with onion and garlic until meat is cooked through. Drain excess fat.
Stir marinara sauce into the beef mixture and simmer for 10 minutes over low heat.
In a medium bowl, combine ricotta cheese, egg, oregano, black pepper, and 1/4 cup of the Parmesan cheese.
Spread 1/2 cup of meat sauce in the bottom of a 9x13 inch baking dish.
Place a layer of zucchini slices over the sauce, followed by a layer of the ricotta mixture, meat sauce, and mozzarella cheese.
Repeat the layers, finishing with a final layer of mozzarella and the remaining Parmesan cheese.
Bake for 30 to 35 minutes until the cheese is golden brown and bubbling.
Allow the lasagna to rest for 15 minutes before serving to let the juices settle and the structure firm up.