In a large bowl, combine the cooked chicken, wilted spinach, ricotta cheese, mozzarella cheese, garlic powder, salt, and black pepper. Mix well until fully combined.

Set the stuffing mixture aside while you prepare the rigatoni.

Bring a large pot of salted water to a boil. Add the rigatoni pasta and cook according to package instructions until al dente, about 10-12 minutes.

Drain the pasta and let it cool slightly. Preheat the oven to 375°F (190°C).

Using a spoon, carefully stuff each rigatoni tube with the chicken and spinach mixture.

Place the stuffed rigatoni in a greased baking dish.

Pour the marinara sauce evenly over the stuffed rigatoni.

Sprinkle the grated parmesan cheese on top of the sauce.

Cover the baking dish with aluminum foil and bake 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.

Garnish with additional cheese or fresh herbs if desired, and enjoy your Stuffed Chicken Spinach Rigatoni!