For the Chicken: Pat the chicken dry and season all over with the salt, pepper, dried oregano and garlic powder. Then, heat a skillet on medium-high and cook the chicken until it reaches an internal temperature of 165°F.
Chop or shred the chicken, then set it aside until needed.
Four Cheese Filling: In the same saucepan you plan to use for preparing the alfredo sauce, heat 1 tablespoon of olive oil over medium-low heat. Once it's hot, add the minced garlic and sauté for 30 seconds. Then immediately remove it from the heat and transfer to a large bowl.
Add the Asiago, Parmesan, Mozzarella and Ricotta cheese to the bowl with the garlic. Stir in the egg, heavy cream and parsley. Mix until fully combined.
Now add the chicken to the cheese mixture and stir to combine.
Preheat an oven to 375°F.
Alfredo Sauce: Using the same saucepan over medium heat, add the butter and melt it, then add the minced garlic and sauté for 30 seconds. Whisk in the flour to create the roux.
Gradually add the milk and heavy cream, stirring until the mixture thickens slightly. Add the Parmesan cheese, salt, and pepper, continuing to stir until the cheese has melted and the sauce has thickened. Remove from the heat and stir in the parsley.
Assembling and Cooking the Stuffed Shells: Spread 1 cup of Alfredo sauce on the bottom of a 9x13 baking dish. Stuff each shell with about 2 tablespoons of the chicken and cheese mixture, then arrange in the dish. Top with the remaining Alfredo sauce, sprinkle with the remaining mozzarella cheese, and bake for 25 minutes. Enjoy!