Prepare for Baking: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish with non-stick cooking spray and set it aside.

Cook Pasta: Cook the pasta according to the package directions until al dente. Drain thoroughly and drizzle with a small amount of oil to prevent sticking.

Make the Cheese Sauce Base: Place a large skillet over medium heat and add the butter. Once melted, add the flour and stir continuously until fully combined and cooked for 1-2 minutes.

Whisk in Milk & Simmer: Gradually add the milk to the flour mixture, whisking constantly until it’s fully incorporated and smooth. Bring the mixture to a gentle simmer, whisking frequently.

Season the Sauce: Reduce the heat to low. Stir in the salt, pepper, paprika, and garlic powder. Mix to combine, then taste and adjust seasonings if needed.

Melt Mozzarella: Turn off the heat and add the shredded mozzarella cheese. Stir until the cheese is completely melted and the sauce is smooth.

Combine Casserole Ingredients: In a large bowl, combine the cooked pasta, cooked chicken, and diced ham. Pour the prepared cheese sauce over the pasta mixture and stir until all ingredients are well combined and evenly coated.

Assemble and Bake: Transfer the entire mixture to the prepared 9×13 inch baking dish and level the top with a spatula. Evenly sprinkle the shredded Swiss cheese over the top of the casserole.

Bake uncovered for 25-30 minutes, or until the cheese on top is slightly golden-brown and the casserole mixture is bubbling around the edges.

Rest and Serve: Remove the casserole from the oven and let it stand for 10 minutes before serving. Garnish with freshly chopped parsley, if desired, and enjoy!