Bring a large pot of salted water to a rolling boil. Carefully add the manicotti tubes and cook them until just al dente, about 6 to 7 minutes. Be gentle when draining to avoid breakage, then rinse with cold water and set aside on a lightly oiled tray to prevent sticking.
In a large mixing bowl, combine the shredded chicken, ricotta cheese, half of the mozzarella, half of the Parmesan, garlic powder, Italian seasoning, salt, and pepper. Mix thoroughly until everything is evenly incorporated and creamy.
Using a spoon or piping bag, carefully fill each manicotti tube with the chicken and cheese mixture. Try not to overfill to prevent pasta splitting during baking.
Spread a thin layer of Alfredo sauce on the bottom of your baking dish to prevent sticking. Arrange the stuffed manicotti tubes in a single layer. Pour the remaining Alfredo sauce evenly over the top. Sprinkle the remaining mozzarella and Parmesan cheeses over everything for a golden, bubbly crust.
Cover the dish with aluminum foil and bake in a preheated oven at 350°F (175°C) for 25 minutes. Remove the foil and bake for an additional 10 minutes or until the cheese is melted and slightly golden.
Once out of the oven, sprinkle freshly chopped parsley over the top for a pop of color and freshness. Serve hot and enjoy.
