Preheat your oven to 350°F (175°C).
Cook the ziti pasta according to package instructions until al dente. Drain and set aside.
In a large bowl, mix together marinara sauce, ricotta cheese, garlic powder, salt, and pepper.
Stir in the cooked ziti and chopped spinach until well combined.
In a 9x13 inch baking dish, spread half of the ziti mixture. Top with half of the mozzarella cheese.
Add the remaining ziti mixture and then top with the rest of the mozzarella and Parmesan cheese.
Cover the baking dish with aluminum foil and bake for 25 minutes.
Remove the foil and bake for an additional 15 minutes, or until the top is golden and bubbly.
Remove from the oven and let it sit for 10 minutes before serving.