Preheat the oven to 375°F (190°C). Cook the lasagna noodles according to package instructions until al dente. Drain and set aside.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and sauté for about 3 minutes until translucent. Stir in the minced garlic and cook for an additional minute.

Add the diced zucchini, bell pepper, and sliced mushrooms to the skillet. Sauté for 5-7 minutes until the vegetables are tender. Stir in the chopped spinach, oregano, basil, salt, and pepper. Cook for another 2 minutes until the spinach wilts. Remove from heat.

In a medium bowl, combine the ricotta cheese, egg, and a pinch of salt and pepper. Mix until smooth.

To assemble the lasagna, spread a thin layer of marinara sauce on the bottom of a 9x13 inch baking dish. Place 3 lasagna noodles on top. Spread half of the ricotta mixture over the noodles, followed by half of the sautéed vegetable mixture. Top with 1/3 of the mozzarella cheese and a layer of marinara sauce.

Repeat the layers: add 3 more noodles, the remaining ricotta mixture, the remaining vegetables, another 1/3 of the mozzarella, and more marinara sauce. Finish with the last 3 noodles, the remaining marinara sauce, the remaining mozzarella, and sprinkle the Parmesan cheese on top.

Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden.

Let the lasagna cool for 10 minutes before slicing and serving.