To begin, set the oven temperature to 325 degrees Fahrenheit (165 degrees Celsius). Prepare a deep baking pan measuring 9x13 inches by greasing it.
Cut the zucchini into thin slices lengthwise. Lightly sprinkle salt on the slices and let them drain in a colander.
To make the meat sauce, heat a large skillet over medium-high heat and cook ground beef with black pepper for 5 minutes while stirring. Then, add green pepper and onion and continue cooking and stirring until the meat is thoroughly cooked and no longer pink.
Incorporate the tomato sauce, tomato paste, wine, basil, and oregano together, and if the sauce appears too thick, you can add a small quantity of hot water. Allow the mixture to reach a boiling point, then lower the heat and let the sauce simmer for approximately 20 minutes. Remember to stir frequently during this process.
In the meantime, mix ricotta cheese, egg, and parsley in a bowl until thoroughly blended.
To assemble lasagna, spread 1/2 of the meat sauce over the bottom of the prepared pan. Layer with 1/2 of the zucchini slices, 1/2 of the ricotta mixture, all of the spinach, followed by all of the mushrooms, then 1/2 of the mozzarella cheese. Repeat by layering in the remaining meat sauce, zucchini slices, ricotta mixture, and mozzarella. Spread Parmesan evenly over the top; cover with foil.
Place the dish in the oven that has been preheated and let it bake for a duration of 45 minutes. After that, uncover the dish, increase the oven temperature to 350 degrees F (175 degrees C), and continue baking for an additional 15 minutes.
Allow the lasagna to rest for 5 minutes before serving.