Preheat your oven to 375°F (190°C).
Cook the lasagna noodles according to the 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 garlic, sautéing until translucent, about 3-5 minutes.
Add the zucchini, red bell pepper, and mushrooms to the skillet. Cook for about 5-7 minutes until softened, then stir in the spinach, oregano, basil, salt, and pepper. Cook for an additional 2-3 minutes. Remove from heat and let cool slightly.
In a mixing bowl, combine the ricotta cheese, egg, and a pinch of salt and pepper. Mix well to create a creamy filling.
Spread a layer of béchamel sauce in the bottom of the 9x13 inch baking dish.
Place 3 lasagna noodles over the sauce, then spread half of the ricotta mixture over the noodles, followed by half of the veggie mixture. Sprinkle with a third of the mozzarella and a third of the Parmesan cheese.
Repeat the layers: sauce, 3 noodles, remaining ricotta, remaining veggie mixture, and half of remaining mozzarella and Parmesan.
Top with the final 3 noodles, remaining béchamel sauce, and the rest of the mozzarella and Parmesan cheese.
Cover the baking dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 20 minutes, or until the cheese is bubbly and golden brown. Let it rest for 10 minutes before serving.