Cook shells according to package directions for al dente.
Preheat oven to 375°F (190°C). Grease a 9x13-inch baking dish.
In a mixing bowl, combine shredded chicken, ricotta,1 cup of mozzarella, Parmesan, egg, garlic powder, Italian seasoning, salt, and pepper. Mix until fully combined.
Spread ½ cup of Alfredo sauce on the bottom of the baking dish.
Stuff each cooked pasta shell with the chicken mixture and place them in the dish.
Pour the remaining Alfredo sauce evenly over the stuffed shells. Sprinkle with remaining ½ cup mozzarella cheese.
Cover with foil and bake for 20 minutes. Then remove foil and bake for an additional 10 minutes until bubbly and golden.
Sprinkle with chopped parsley and serve warm.