Preheat your oven to 375°F (190°C). Cook lasagna noodles in a large pot of salted boiling water until al dente (8-10 minutes). Drain, rinse with cold water, and set aside.

In a large skillet, heat olive oil over medium heat. Add chopped onions and minced garlic, sauté for 3-4 minutes until softened.

Incorporate diced zucchini, sliced bell peppers, and mushrooms into the skillet. Cook for 5-7 minutes until tender.

Stir in fresh spinach, allowing it to wilt for 1-2 minutes. Add marinara sauce, basil, and oregano, and simmer for 5 minutes.

In a bowl, mix ricotta cheese, a beaten egg, salt, and pepper until smooth.

Spread a layer of marinara in a baking dish. Alternate layers of noodles, ricotta mixture, sauce, and mozzarella. Finish with noodles and sauce topped with mozzarella and Parmesan.

Cover with foil and bake for 25 minutes. Remove foil and bake for an additional 15 minutes until cheese is bubbling and golden brown.

Let the lasagna rest for 10 minutes before slicing and serving.