Cook the ziti pasta according to package instructions until al dente. Drain and set aside.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté until translucent, about 3-4 minutes.
Stir in the minced garlic, chopped bell pepper, zucchini, and sliced mushrooms. Cook for another 5-7 minutes until the vegetables are tender.
Pour in the crushed tomatoes, and season with dried basil, oregano, salt, and pepper. Let it simmer for about 10 minutes.
Stir in the fresh spinach until just wilted, then remove from heat.
In a large bowl, combine the cooked ziti, vegetable sauce, ricotta cheese, and half of the mozzarella cheese. Mix well until everything is evenly coated.
Transfer the mixture into a greased 9x13 inch baking dish. Top with the remaining mozzarella cheese and Parmesan cheese.
Cover with foil and bake in the preheated oven for 25 minutes. Remove the foil and bake for an additional 10-15 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let it cool for a few minutes before serving.
Notes
Garnish with fresh basil leaves and serve with a side salad and garlic bread for a complete meal.