Preheat your oven to 375°F (190°C).
In a large saucepan, heat olive oil over medium heat. Add garlic, mushrooms, bell peppers, and zucchini. Cook until tender.
Add spinach and cook until wilted. Season with salt and pepper.
In a baking dish, spread a thin layer of marinara sauce. Layer with lasagna noodles, ricotta cheese, vegetable mixture, mozzarella cheese, and Parmesan cheese. Repeat layers.
Top with remaining marinara sauce and mozzarella cheese.
Cover with foil and bake for 40 minutes. Remove foil and bake for an additional 20 minutes, or until cheese is golden and bubbly.
Let lasagna cool for 10 minutes before serving.