Preheat the oven to 375°F (190°C).

Bring a large pot of salted water to a boil. Cook the lasagna noodles according to package directions until al dente. Drain and lay them flat on a tray to prevent sticking.

Heat the olive oil in a large skillet over medium heat. Add the diced bell pepper, zucchini, and carrots. Season lightly with salt and pepper. Sauté for 5–7 minutes until the vegetables are tender and starting to brown. Remove from heat and stir in the Italian seasoning.

Lightly spread a thin layer of marinara sauce across the bottom of a 9x13-inch (or similar) baking dish.

Place 3 lasagna noodles over the sauce in a single layer. Spoon half the ricotta over the noodles and spread it gently. Top the ricotta with half of the sautéed vegetables. Sprinkle with one-third of the shredded mozzarella and a light dusting of Parmesan.

Repeat the layers: 3 noodles, remaining ricotta, remaining vegetables, another third of the mozzarella, and Parmesan.

Finish with the final 3 noodles, spread the remaining marinara sauce over them, and top with the remaining mozzarella and Parmesan.

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

Remove the foil and bake uncovered for 12–15 minutes, until the cheese is bubbly and golden.

Let the lasagna rest for 8–10 minutes before cutting into 8 servings.