Preheat your oven to 375°F (190°C).,

In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add 1 chopped onion, 2 minced garlic cloves, and sauté for 3-4 minutes until translucent.,

Add 2 cups of chopped spinach, 1 cup of chopped mushrooms, and 1 cup of diced bell peppers. Cook for an additional 5-7 minutes until the vegetables are tender.,

Stir in 1 cup of ricotta cheese, 1/2 cup of grated Parmesan cheese, and season with salt and pepper to taste. Mix well and remove from heat.,

In a separate bowl, combine 2 cups of marinara sauce with 1 teaspoon of dried oregano and 1 teaspoon of dried basil.,

Spread a thin layer of the marinara sauce in the bottom of a 9x13 inch baking dish.,

Layer 3 lasagna noodles on top of the sauce, then add half of the vegetable mixture, followed by a layer of marinara sauce, and sprinkle with 1 cup of shredded mozzarella cheese.,

Repeat the layers again: noodles, remaining vegetable mixture, marinara sauce, and another layer of mozzarella cheese.,

Top with the final 3 lasagna noodles and cover with the remaining marinara sauce and 1 cup of mozzarella cheese.,

Cover the dish with aluminum foil and bake for 25 minutes. Then remove the foil and bake for an additional 15-20 minutes until the cheese is bubbly and golden brown.,

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