Prepare the pasta according to the package directions until al dente. While the pasta is cooking, preheat your oven to 400°F.

Season both sides of the chicken pieces with Cajun seasoning. In a large skillet, heat the olive oil over medium-high heat. Once the oil is hot, add the chicken and cook for 6–7 minutes, flipping halfway through, until fully cooked and golden on the outside.

In a medium saucepan, melt the butter over medium heat. Whisk in the flour and cook, stirring constantly, for about 1 minute—watch carefully to prevent burning. Gradually pour in the milk while whisking and bring the mixture to a gentle simmer, stirring frequently to avoid overflow. Let it simmer for 2–3 minutes, then remove from heat. Add both the Parmesan and cheddar cheese, stirring until the sauce is smooth and free of lumps.

Add the cooked pasta and Alfredo sauce to the skillet with the chicken, tossing everything together to ensure the pasta is fully coated. Transfer the mixture to a greased 13x9-inch baking dish and sprinkle the 1/2 cup of shredded cheddar cheese evenly on top. Bake in the preheated oven for 5–10 minutes, or until the cheese has melted. For a golden brown finish, switch to broil for a minute or two—just keep a close eye on it.

Serve immediately, garnished with freshly chopped parsley if desired.