Heat the olive oil in a large skillet over medium heat. Sauté the onion and garlic until soft and fragrant, about 3-4 minutes.

Stir in the zucchini, bell pepper, and spinach. Cook until the vegetables are tender, about 5 minutes.

Add the oregano, basil, salt, and pepper to the skillet. Stir to combine.

Cook the lasagna noodles according to package instructions.

In a mixing bowl, combine the ricotta cheese, half of the mozzarella, and the Parmesan cheese.

Spread a thin layer of marinara sauce on the bottom of the baking dish.

Layer noodles, cheese mixture, sautéed vegetables, and more sauce, repeating until ingredients are used.

Finish with a layer of noodles and remaining marinara sauce, then sprinkle the rest of the mozzarella on top.

Cover the dish with aluminum foil and bake in a preheated oven at 375°F (190°C) for 30 minutes.

Remove the foil in the last 15 minutes to allow the cheese to brown nicely.

Let the lasagna sit for 10-15 minutes before slicing.