Lay the zucchini slices on paper towels, sprinkle with salt, and let sit for 20 minutes to draw out moisture. Pat dry thoroughly.
Preheat the oven to 375°F. Brown the ground beef with the onion in a large skillet over medium-high heat, breaking it up as it cooks. Add the garlic and cook 1 minute more.
Drain excess fat and stir in the marinara, Italian seasoning, and black pepper. Simmer for 5 minutes.
In a bowl, mix the ricotta, egg, and parmesan until smooth.
In a 9x13 baking dish, spread a thin layer of meat sauce. Layer zucchini slices, half the ricotta mixture, more meat sauce, and a third of the mozzarella.
Repeat the layers, finishing with zucchini, the last of the meat sauce, and the remaining mozzarella on top.
Bake uncovered for 35-40 minutes until bubbly and golden. Let rest for 10 minutes, then top with fresh basil before serving.