Preheat your oven to 325°F (165°C) and grease a deep 9x13-inch baking pan.
Slice zucchini lengthwise into very thin strips, about ⅛ inch thick. Sprinkle both sides with salt and place the slices in a colander to drain for 20-30 minutes. Pat them dry with paper towels to remove excess moisture.
In a large skillet, cook the ground beef with black pepper over medium-high heat for 5 minutes, breaking it apart as it cooks. Add diced green bell pepper and onion, and sauté until the beef is browned and the vegetables are tender.
Stir in tomato sauce, tomato paste, red wine, fresh basil, and oregano. Add hot water if the sauce is too thick. Bring to a boil, then reduce the heat and simmer for 20 minutes, stirring occasionally.
In a medium bowl, mix ricotta cheese, egg, and parsley until smooth. Set aside.
Begin assembling the lasagna in the prepared pan. Spread half of the meat sauce on the bottom of the pan. Add a layer of zucchini slices, followed by half of the ricotta mixture.
Spread all of the spinach and mushrooms over the ricotta layer, then sprinkle half of the shredded mozzarella cheese on top. Repeat the layers with the remaining meat sauce, zucchini slices, ricotta mixture, and mozzarella cheese.
Sprinkle grated Parmesan cheese evenly over the top layer. Cover the pan with foil.
Bake in the preheated oven for 45 minutes. Remove the foil, increase the oven temperature to 350°F (175°C), and bake for another 15 minutes until the cheese is melted and golden brown.
Let the lasagna cool for 5-10 minutes before slicing and serving.
