Bring a large pot of salted water to a boil. Cook the pasta shells until al dente according to package directions. Drain and allow them to cool slightly.
In a large bowl, combine shredded chicken, softened cream cheese, mozzarella cheese, half of the Parmesan cheese, Cajun seasoning, salt, and pepper. Mix until smooth and evenly combined.
Spoon the filling generously into each cooked pasta shell.
Arrange the stuffed shells in a lightly greased baking dish in a single layer.
Heat butter or oil in a small saucepan over medium heat. Stir in the remaining Cajun seasoning and pour in the chicken broth. Simmer for 2–3 minutes until well blended.
Pour the sauce evenly over the stuffed shells. Sprinkle the remaining Parmesan cheese over the top.
Cover the dish with foil and bake at 375°F (190°C) for 20 minutes.
Remove the foil and continue baking for another 10–15 minutes until the cheese is melted and lightly golden.
Let the Creamy Cajun Chicken Stuffed Shells rest for 5 minutes before garnishing with fresh parsley and serving.