Oven to 350 degrees and spray a 9×13 casserole dish with nonstick spray.
The chicken in the bottom of the dish followed by the ham and finally the swiss cheese.
The butter over medium heat, in a medium saucepan, and add garlic as it melts. Keep stirring with a rubber spatula to avoid burning.
In salt, pepper, Dijon mustard, smoked paprika, and lemon juice.
In the flour and cook for 1 minute.
The milk, slowly. Whisk often to keep clumps from forming. Turn the heat to high and cook until the sauce thickens and boils completely.
The finished sauce over the base layer already in the dish.
The topping ingredients, in a small bowl, until the butter is evenly distributed over the crumbs.
Over the top of the dish and bake for 45 minutes at 350 degrees. Allow to cool for 10 minutes before serving so the sauce with thicken just a bit.
