Preheat your oven to 375°F (190°C). Lightly oil a 9x13-inch baking dish.

Cook the lasagna noodles according to package directions. Drain and lay them flat to prevent sticking.

Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the diced red bell pepper, sliced zucchini, yellow squash, and mushrooms. Sauté until the vegetables are tender and starting to brown, about 6–8 minutes.

Stir in the 2 cups spinach and cook just until wilted. Season the vegetable mixture with salt and pepper to taste. Remove from heat.

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

Place three lasagna noodles across the sauce. Spoon half the vegetable mixture evenly over the noodles. Dollop and gently spread half the ricotta over the vegetables. Sprinkle about one-third of the shredded mozzarella, then add more marinara sauce to cover.

Repeat the layering: three noodles, remaining vegetables, remaining ricotta, another third of the mozzarella, and sauce. Finish with the last three noodles.

Spread remaining marinara sauce over the top. Sprinkle with the remaining mozzarella and the grated Parmesan.

Cover the dish tightly with foil and bake for 25 minutes.

Remove the foil and bake uncovered for an additional 15 minutes, or until the cheese is bubbly and lightly golden.

Let the lasagna rest for 10 minutes before slicing. Garnish with fresh basil leaves and serve.