Preheat your oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.
Bring a large pot of salted water to a boil. Add the jumbo shells and cook for 1-2 minutes less than package directions (al dente). Drain and rinse with cool water to stop cooking.
In a large mixing bowl, combine the shredded chicken, ricotta cheese, 1 cup of the mozzarella cheese, Parmesan cheese, beaten egg, Italian seasoning, garlic powder, salt, and pepper. Mix until well combined.
Stuff each cooked pasta shell generously with the chicken and cheese mixture. Arrange the filled shells in the prepared baking dish.
In a medium saucepan, melt the butter over medium heat. Add the minced garlic and sauté for 1 minute until fragrant.
Pour in the heavy cream and bring to a gentle simmer. Cook for 5-7 minutes, stirring occasionally, until the sauce thickens slightly. Season with salt and pepper to taste.
Pour the garlic butter cream sauce evenly over the stuffed shells in the baking dish.
Sprinkle the remaining 1 cup of mozzarella cheese over the top.
Bake for 20-25 minutes, or until the cheese is melted and bubbling. For a golden crust, broil for the last 2-3 minutes.
Garnish with fresh chopped parsley before serving.