Bring a large pot of salted water to a rolling boil. Add the jumbo shells and cook until just firm to the bite (al dente). Drain thoroughly and set aside to cool slightly before handling.

In a mixing bowl, toss the cooked chicken with half of the Cajun seasoning blend until evenly coated. Set aside while preparing the sauce.

In a large skillet set over medium heat, melt the butter. Add the minced garlic and sauté until aromatic, about 1 minute. Pour in the heavy cream and bring to a gentle simmer. Sprinkle in the Parmesan cheese along with the remaining Cajun seasoning. Stir continuously until the sauce becomes smooth and begins to thicken. Adjust seasoning with salt and pepper to taste.

In a separate bowl, combine the spiced chicken, half of the prepared Alfredo sauce, shredded mozzarella, and ricotta cheese if using. Stir until the mixture is well blended.

Coat a baking dish lightly with oil or non-stick spray. Fill each cooked pasta shell with a generous spoonful of the chicken mixture and arrange them snugly in the dish. Pour the reserved Alfredo sauce evenly over the filled shells. Scatter additional mozzarella cheese on top.

Cover the dish with foil and bake in a preheated oven at 375°F (190°C) for 20 minutes. Remove the foil and broil for an additional 2 to 3 minutes, or until the top is golden and the cheese is bubbling.

Sprinkle chopped parsley over the baked shells just before serving. Serve hot.