Step 1: Cook the Pasta and Season the Protein
Preheat oven to 375°F (190°C). Grease a 9×13 inch (23x33cm) baking dish. Cook pasta in salted boiling water for 2-3 minutes LESS than package directions for al dente. Drain and set aside. In a bowl, toss the cubed chicken with 1 tablespoon of the prepared Cajun seasoning. Set aside.

Step 2: Sear the Sausage and Chicken
In a large, deep skillet or Dutch oven, heat olive oil over medium-high heat. If using Andouille sausage, add the slices and cook for 2-3 minutes per side until browned. Remove to a plate. In the same skillet, add the seasoned chicken in a single layer (work in batches if needed). Sear for 3-4 minutes per side until golden brown but not cooked through. Remove to the plate with the sausage.

Step 3: Sauté the Holy Trinity
In the same skillet, melt 3 tablespoons of butter over medium heat. Add the diced onion, green bell pepper, and celery (the Holy Trinity). Cook, stirring occasionally, for 8-10 minutes until the vegetables are very soft and fragrant. Add the minced garlic and cook for 1 more minute.

Step 4: Build the Cajun Roux Sauce
Push the vegetables to the sides. In the center, melt 4 tablespoons of butter. Sprinkle the flour over the butter and whisk constantly for 2-3 minutes to form a copper-colored roux (this is the flavor foundation). Gradually whisk in the warm milk and chicken broth until completely smooth and thickened. Whisk in the remaining Cajun seasoning.

Step 5: Finish the Creamy Sauce
Reduce heat to low. Whisk in the cubed cream cheese and heavy cream until the sauce is completely smooth and luxurious. Stir in the Worcestershire sauce and hot sauce. Taste and adjust seasoning, adding more salt, cayenne, or hot sauce as desired. Remove from heat.

Step 6: Combine All Components
To the skillet with the sauce, add the drained al dente pasta, seared chicken, Andouille sausage, and any accumulated juices. Gently fold everything together. Stir in 2 cups of the cheddar cheese, all of the Pepper Jack cheese, and ½ cup of the Parmesan cheese until the cheeses are melted and distributed.

Step 7: Assemble and Add the Crunchy Topping
Pour the mixture into the prepared baking dish, spreading it evenly. Sprinkle the remaining 1 cup of cheddar cheese and ¼ cup of Parmesan over the top. In a small bowl, mix the Panko breadcrumbs, melted butter, and 1 tablespoon of Cajun seasoning. Sprinkle this mixture evenly over the cheese.

Step 8: Bake to Golden, Bubbling Perfection
Place the dish on a rimmed baking sheet. Bake, uncovered, for 25-35 minutes, or until the topping is deep golden brown, the casserole is bubbling vigorously around the edges, and the center is hot.

Step 9: Garnish and Serve
Remove from oven and let rest for 10-15 minutes to allow the sauce to set slightly for clean serving. Garnish generously with sliced green onions and fresh parsley. Serve hot, with extra hot sauce on the side for those who dare.