Preheat your oven to 350°F and lightly grease your casserole dish with cooking spray. This simple step keeps cleanup easy and prevents sticking.

Spread the shredded chicken evenly across the bottom of your prepared dish, followed by the diced ham. Layering like this ensures every bite gets that satisfying combo of chicken and ham.

This luxurious sauce ties everything together! Start by melting the butter in a saucepan over medium heat. Gradually whisk in the flour, cooking for 1–2 minutes until it forms a smooth paste. Slowly add the milk, whisking to avoid lumps, and simmer until the mixture thickens, about 3–5 minutes. Stir in Dijon mustard, lemon juice, garlic powder, and salt, then remove the pan from heat. Finally, fold in the Swiss and Parmesan cheeses until melted.

Carefully pour the creamy cheese sauce over the chicken and ham, making sure to distribute it evenly. This ensures that the flavors soak into every layer.

Mix the panko breadcrumbs with melted butter in a small bowl. Sprinkle the topping generously over the casserole for that irresistible crunch.

Bake the casserole uncovered for 30–35 minutes or until the top is golden brown and bubbling. Remove it from the oven and allow it to rest for about 5–10 minutes before serving. This helps the layers set and makes scooping easier.