1. 1. Prepare the Pasta Shells: Bring a large pot of salted water to a rolling boil. Add the jumbo pasta shells and cook according to package directions until al dente. You want them firm enough to handle without tearing. Drain the shells and rinse them with cold water to prevent sticking. Lay them out on a baking sheet or clean surface to cool slightly while you prepare the filling.

2. 2. Create the Creamy Filling: In a large mixing bowl, combine the shredded cooked chicken, thoroughly squeezed dry spinach, ricotta cheese, 1 cup of shredded mozzarella cheese, 1/2 cup of grated Parmesan cheese, the large egg, garlic powder, onion powder, salt, and black pepper. Mix everything together until all ingredients are well combined and evenly distributed.

3. 3. Preheat Oven and Prepare Baking Dish: Preheat your oven to 375 F (190 C). Lightly grease a 9×13-inch baking dish with cooking spray or a little butter.

4. 4. Assemble the Stuffed Shells: Pour about half of your Alfredo sauce into the bottom of the prepared baking dish, spreading it evenly. This will create a nice bed for the shells and prevent them from sticking. Carefully take each cooked jumbo shell and spoon a generous amount of the chicken and spinach filling into it. Arrange the filled shells snugly in a single layer in the baking dish.

5. 5. Add More Sauce and Cheese: Once all the shells are filled and arranged, pour the remaining Alfredo sauce evenly over the top of the shells. If your Alfredo sauce is very thick, you can thin it slightly with 1/4 cup of milk before pouring. Sprinkle the remaining 1/2 cup of shredded mozzarella cheese and 2 tablespoons of grated Parmesan cheese over the sauced shells.

6. 6. Bake Until Golden and Bubbly: Cover the baking dish loosely with aluminum foil. Bake for 20 minutes. Then, remove the foil and continue baking for another 10-15 minutes, or until the cheese is melted, bubbly, and lightly golden brown, and the filling is heated through.

7. 7. Rest and Serve: Once baked, remove the dish from the oven and let it rest for 5-10 minutes before serving. This allows the sauce to set slightly and prevents the filling from spilling out when serving. Garnish with fresh chopped parsley, if desired.