Preheat the oven to 375°F (190°C).
Cook the lasagna noodles according to package instructions; drain and set aside.
In a skillet, heat olive oil over medium heat.
Add chopped bell pepper and sliced mushrooms; sauté for 5 minutes.
Incorporate the zucchini and spinach; cook until wilted.
Season the vegetables with salt, pepper, and Italian seasoning.
Spread a thin layer of marinara sauce at the bottom of a baking dish.
Layer three lasagna noodles over the sauce.
Spread half of the ricotta cheese, followed by half of the sautéed vegetables.
Add a layer of mozzarella cheese and a bit more marinara sauce.
Repeat layers, finishing with noodles, marinara sauce, and remaining mozzarella and parmesan cheese on top.
Cover with foil and bake for 30 minutes; remove foil and bake an additional 15 minutes until golden.