Preheat the oven to 375°F (190°C).

Cook the lasagna noodles in a pot of salted boiling water according to package instructions until al dente, about 8-10 minutes. Drain and rinse briefly under cold water.

In a mixing bowl, combine ricotta cheese, salt, black pepper, and dried oregano. Stir well to create a filling.

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

Arrange three lasagna noodles over the marinara sauce in the baking dish, slightly overlapping.

Spread half of the ricotta mixture over the noodles.

Sprinkle half of the zucchini, mushrooms, and bell peppers over the ricotta layer, followed by another layer of marinara sauce.

Repeat the layering process with three more noodles, another spread of the ricotta mixture, and the remaining vegetables, topped with marinara sauce.

Lay the last three noodles on top, and pour the remaining marinara sauce over them, spreading evenly.

Sprinkle shredded mozzarella cheese evenly over the lasagna.

Cover the baking dish tightly with aluminum foil and bake for 30 minutes.

Remove the foil and bake for an additional 15 minutes until the top is bubbling and golden brown.

Let cool for 10 minutes before slicing and serving.