Preheat the oven to 375°F (190°C) and cook the lasagna noodles according to package instructions until al dente. Drain and set aside.

In a large skillet, heat olive oil over medium heat. Add chopped onion and minced garlic, sautéing for 3-4 minutes until translucent.

Introduce chopped zucchini, red and yellow bell peppers, and sliced mushrooms. Cook for 5-7 minutes until tender.

Stir in fresh spinach until wilted. Add marinara sauce, dried basil, and oregano. Simmer for 5 minutes.

In a separate bowl, combine ricotta cheese, whisked egg, salt, and pepper. Mix until creamy.

In a baking dish, layer vegetable sauce, three noodles, half of the ricotta mixture, and 1 cup of mozzarella cheese.

Repeat layering with remaining ingredients, ending with noodles and marinara sauce on top.

Cover with foil and bake for 25 minutes, then remove foil and bake for another 15 minutes until bubbly and golden brown.

Let the lasagna rest for 10 minutes before slicing.