Preheat the oven to 375°F (190°C).
Cook the ziti pasta according to package instructions until al dente.
In a large bowl, combine cooked ziti, marinara sauce, ricotta cheese, spinach, garlic powder, salt, and pepper.
Transfer half of the ziti mixture to a greased baking dish.
Sprinkle half of the mozzarella and Parmesan cheese on top of the first layer.
Add the remaining ziti mixture on top, then top with the remaining cheeses.
Cover with foil and bake for 20 minutes.
Remove the foil and bake for an additional 15-20 minutes until bubbly and golden.
Let it cool for a few minutes before serving.