Preheat oven to 375°F (190°C).
In a large saucepan, sauté zucchini, bell peppers, and onion until tender.
Add spinach and cook until wilted.
Spread a thin layer of marinara sauce in a baking dish.
Layer with lasagna noodles, vegetable mixture, vegan ricotta, and marinara sauce. Repeat layers.
Top with vegan mozzarella.
Cover with foil and bake for 40 minutes. Remove foil and bake for another 20 minutes or until bubbly.
Let stand for 10 minutes before serving.