Preheat your oven to 375°F (190°C). Cook lasagna noodles until al dente, about 8-10 minutes. Drain and rinse with cold water.

In a skillet, heat olive oil over medium heat. Sauté onion and garlic until soft and fragrant, about 4-5 minutes.

Add zucchini, red bell pepper, and yellow bell pepper. Sauté for 5-7 minutes until tender.

Stir in spinach until wilted, then add marinara sauce, basil, and oregano. Simmer for 5 minutes.

Mix ricotta with egg, salt, and pepper in a bowl until smooth.

In a baking dish, layer vegetable sauce, noodles, ricotta mixture, and mozzarella cheese.

Repeat layering with remaining ingredients. Finish with cheese on top.

Cover with foil and bake for 25 minutes, uncover and bake for another 15 minutes until golden.

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