Preheat oven to 375°F (190°C).
In a saucepan, heat olive oil over medium heat. Add garlic and sauté until fragrant.
Add chopped zucchini, bell peppers, and mushrooms. Cook until tender.
Mix ricotta cheese with chopped spinach in a bowl. Season with salt and pepper.
Spread a thin layer of marinara sauce on the bottom of a baking dish.
Layer lasagna noodles, ricotta mixture, vegetable mixture, marinara sauce, mozzarella, and Parmesan. Repeat layers.
Cover with foil and bake for 40 minutes. Remove foil and bake for an additional 20 minutes until cheese is bubbly and golden.
Let lasagna cool for 10 minutes before serving.