Cook the jumbo pasta shells in a large pot of salted boiling water according to package instructions until al dente. Drain and set aside to cool slightly.
In a mixing bowl, combine the shredded chicken, ricotta cheese, 1/2 cup of mozzarella cheese, 1/4 cup of Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper. Mix until well combined.
Spread 1 cup of the Alfredo sauce evenly over the bottom of a 9x13 inch baking dish.
Carefully stuff each cooked pasta shell with the chicken and cheese mixture, then place them seam-side up in the baking dish.
Pour the remaining Alfredo sauce over the stuffed shells, covering them generously.
Sprinkle the top with the remaining mozzarella and Parmesan cheese.
Cover the dish with aluminum foil and bake in the preheated oven for 25 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the cheese is melted and bubbly.
Once baked, remove from the oven and let it cool for a few minutes. Garnish with fresh parsley before serving.
Notes
Feel free to use store-bought Alfredo sauce for convenience.