Preheat oven to 375°F (190°C). Cook lasagna noodles according to package directions until al dente, about 8–10 minutes. Drain and lay flat on parchment paper to prevent sticking.

In a large skillet, heat 2 tablespoons of olive oil over medium heat. Add chopped onion and minced garlic, sauté until onion is translucent, about 3–4 minutes.

Add chopped zucchini, red and yellow bell peppers, and sliced mushrooms. Stir and cook until vegetables are tender, about 5–7 minutes.

Stir in fresh spinach until wilted, about 1–2 minutes, then pour in marinara sauce along with dried basil and oregano. Let it simmer for 5 minutes.

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

In a 9x13 inch baking dish, spread a thin layer of vegetable sauce at the bottom. Layer 3 noodles, half of the ricotta mixture, and half of the vegetable mixture. Sprinkle 1 cup of mozzarella cheese.

Continue layers with 3 more noodles, remaining ricotta mixture, rest of vegetable sauce, and another cup of mozzarella.

Top with a final set of noodles, spreading remaining vegetable sauce and sprinkle remaining mozzarella and grated Parmesan.

Cover with foil and bake for 25 minutes, then remove foil and bake uncovered for another 15 minutes.

Let lasagna rest for about 10 minutes before slicing.