Cook the lasagna noodles in a large pot of salted water until al dente. Drain and lay them flat to prevent sticking.

Heat the olive oil in a skillet over medium heat. Add the onion and garlic and cook for 3 minutes until softened.

Add the zucchini and red bell pepper to the skillet. Cook for 5 minutes until they start to soften. Stir in the spinach and cook until wilted. Season with salt and black pepper, then remove from heat.

Spread 1 cup of marinara sauce in the bottom of a 9x13 baking dish. Lay 3 noodles over the sauce.

Spread half the ricotta cheese over the noodles, then half the vegetable mixture. Sprinkle with one third of the mozzarella and Parmesan.

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

Top with the final 3 noodles, the remaining marinara sauce, and the last of the mozzarella and Parmesan.

Bake at 375°F for 30 minutes until the cheese is bubbly and lightly browned. Let it rest for 10 minutes before slicing. Garnish with fresh basil leaves when serving.