Preheat your oven to 375°F (190°C). Cook the ziti pasta according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet, heat olive oil over medium heat. Add diced onion and sauté for about 5 minutes until translucent.

Incorporate minced garlic and cook for about 1 minute until fragrant. Then add red and green bell peppers, zucchini, and mushrooms, sauté for about 7-10 minutes until tender.

Stir in fresh spinach and let it wilt for about 2 minutes. Sprinkle in oregano, basil, salt, and pepper, mixing well to combine.

Combine the warm ziti pasta with the sautéed vegetable mixture and marinara sauce, mixing until evenly coated.

Layer half of the ziti mixture into a 9x13-inch baking dish. Dollop half of the ricotta, followed by half of the mozzarella and Parmesan.

Repeat the layering process with the remaining ziti mixture and cheeses.

Bake in the preheated oven for 25-30 minutes until the cheese bubbles and is golden brown.

Cool for 10 minutes, then garnish with fresh basil leaves before serving.