Preheat your oven to 350°F (175°C) and grease a 9-by-13-inch baking dish with some butter.
Season the chicken cutlets with salt and pepper, then melt 1 tablespoon of butter in a skillet over medium heat.
Cook the cutlets for about 2-3 minutes on each side until they're nicely browned.
Arrange the browned chicken cutlets in the baking dish.
Layer each cutlet with a slice of ham and Swiss cheese.
In a bowl, mix the cream of chicken soup, milk, and mustard.
Pour this creamy mixture evenly over the chicken cutlets.
Combine the breadcrumbs and grated Parmesan cheese in a small bowl, then sprinkle over the top of the casserole.
Bake for 25-30 minutes until bubbly and golden on top.