Bring a large pot of salted water to a boil. 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 garlic, sautéing for about 2-3 minutes until fragrant and translucent.
Add the bell pepper, zucchini, and yellow squash to the skillet. Sauté for another 5-7 minutes until they are tender. Stir in the chopped spinach and cook for an additional 1-2 minutes until wilted.
Stir in the marinara sauce, dried basil, dried oregano, salt, and pepper. Let the mixture simmer for about 5 minutes.
In a large mixing bowl, combine the cooked ziti, veggie sauce mixture, and ricotta cheese. Stir until evenly incorporated.
Transfer half of the ziti mixture to a 9x13 inch baking dish, spreading it evenly. Add half of the shredded mozzarella on top. Layer the remaining ziti mixture over it, then top with the rest of the mozzarella and sprinkle with grated Parmesan.
Cover the baking dish with aluminum 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 brown.
Let it cool for a few minutes, then garnish with fresh basil leaves before serving.
Notes
Feel free to add more vegetables or adjust the cheese to your liking.