Preheat your oven to 375°F (190°C).
Cook lasagna noodles according to package instructions; drain and set aside.
In a skillet, heat olive oil and sauté onions and garlic until fragrant.
Add chopped bell peppers, zucchini, and spinach; cook until tender.
Stir in marinara sauce and season with salt, pepper, and Italian herbs.
In a baking dish, spread a thin layer of the vegetable sauce.
Layer noodles over the sauce, followed by ricotta and mozzarella.
Repeat layering until all ingredients are used, finishing with mozzarella.
Cover with foil and bake for 30 minutes.
Remove foil and bake for an additional 15 minutes until cheese is bubbly.