Preheat your oven to 350°F (175°C). Bring a large pot of salted water to a boil.
Carefully add the 12 jumbo pasta shells and cook until al dente, about 10-12 minutes. Drain and rinse with cold water to stop cooking. Set aside on a lightly oiled surface to prevent sticking.
In a large mixing bowl, combine shredded cooked chicken, ricotta cheese, 1/2 cup mozzarella, grated Parmesan, garlic powder, Italian seasoning, salt, and pepper. Mix thoroughly until well combined.
Using a spoon or small spatula, gently fill each pasta shell with the chicken and cheese mixture. Be careful not to overfill.
Spread 1 cup of Alfredo sauce evenly on the bottom of the baking dish. Arrange stuffed shells in a single layer on top of the sauce.
Pour the remaining 1 cup Alfredo sauce over the shells, coating each one. Sprinkle the remaining mozzarella cheese on top.
Cover the dish with aluminum foil and bake for 25 minutes. Remove foil and bake an additional 10 minutes until cheese is melted and slightly browned.
Remove from oven and let cool a few minutes. Garnish with fresh chopped parsley. Serve warm and enjoy.