Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells according to the package instructions until al dente. Drain and set aside.
In a large mixing bowl, combine the shredded chicken, ricotta cheese, half of the mozzarella cheese, garlic powder, Italian seasoning, salt, and pepper. Mix until well combined.
Stuff each cooked pasta shell with the chicken and cheese mixture and place them in a 9x13-inch baking dish, open side up.
Pour 1 cup of Alfredo sauce evenly on the bottom of the baking dish. Then pour the remaining Alfredo sauce over the stuffed shells and sprinkle the remaining mozzarella and Parmesan cheese on top.
Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10-15 minutes until the cheese is bubbly and golden.
Let it cool for a few minutes before garnishing with fresh parsley and serving.