Preheat oven to 375°F (190°C). Prepare zucchini by thinly slicing lengthwise; you can lightly salt and drain them for 30 minutes to reduce water content, then pat dry.

In a large skillet, heat olive oil over medium heat. Add ground meat, onion, and garlic, cooking until meat is browned and vegetables are tender. Drain excess fat.

Stir in crushed tomatoes, tomato paste, oregano, and half of the fresh basil. Season with salt and pepper, then simmer for 15-20 minutes, allowing the sauce to thicken slightly.

In a separate bowl, combine ricotta cheese, grated Parmesan, egg, and the remaining fresh basil. Season with salt and pepper, and mix until well combined.

Spread a thin layer of meat sauce on the bottom of a large baking dish. Arrange a layer of zucchini slices over the sauce, slightly overlapping.

Top the zucchini with half of the ricotta mixture, then sprinkle with a third of the mozzarella cheese. Repeat the layers: meat sauce, zucchini, remaining ricotta, and another third of the mozzarella.

Finish with a final layer of zucchini, the rest of the meat sauce, and the remaining mozzarella cheese. Cover the baking dish loosely with foil.

Bake for 30 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden brown. Let it rest for 10-15 minutes before serving.