Boil a large pot of salted water. Add the jumbo pasta shells and cook according to package instructions until al dente. Drain and set aside to cool slightly.

In a mixing bowl, combine the cooked chicken, ricotta cheese, shredded mozzarella, grated Parmesan, garlic powder, Italian seasoning, salt, and pepper. Mix well until all ingredients are evenly incorporated.

In a skillet over medium heat, melt the butter. Add the minced garlic and sauté for about 1 minute until fragrant, being careful not to burn it.

Pour in the heavy cream and bring to a gentle simmer. Stir in the grated Parmesan cheese, salt, and pepper. Continue to cook, stirring frequently, until the sauce thickens slightly, about 5-7 minutes.

Preheat your oven to 350°F (175°C). Spread a thin layer of Alfredo sauce on the bottom of a baking dish.

Stuff each cooked shell with the chicken filling and place them in the baking dish, open side up.

Once all shells are filled, pour the remaining Alfredo sauce over the top, ensuring all shells are covered.

Sprinkle the additional mozzarella and Parmesan cheese on top.

Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.

Let the dish cool for a few minutes before serving.