This Vegetable Lasagna is a comforting, oven-baked dinner layered with tender pasta, sautéed vegetables, creamy ricotta, and plenty of marinara and melted cheese.
Preheat the oven to 375°F. Lightly grease a 9×13-inch baking dish and set aside.
Bring a large pot of salted water to a boil. Cook the lasagna noodles according to package directions until just al dente. Drain and lay flat to prevent sticking.
Heat the olive oil in a large skillet over medium heat. Add the diced onion and cook for 2–3 minutes until softened. Stir in the garlic, red bell pepper, mushrooms, and zucchini. Cook for 5–7 minutes, until the vegetables are tender and most of the moisture has cooked off. Add the spinach and cook just until wilted. Stir in the oregano and basil, then remove from heat.
In a medium bowl, mix together the ricotta cheese, egg, and Italian seasoning until smooth.
Spread a thin layer of marinara sauce over the bottom of the prepared baking dish. Arrange a layer of noodles on top, followed by a portion of the ricotta mixture, sautéed vegetables, marinara sauce, and a sprinkle of mozzarella and parmesan. Repeat the layers until all ingredients are used, finishing with sauce and cheese on top.
Cover the dish loosely with foil and bake for 35 minutes. Remove the foil and bake for an additional 15–20 minutes, until the cheese is melted and lightly golden.
Remove the lasagna from the oven and let it rest for 10–15 minutes before slicing and serving.