Preheat oven to 350 degrees F. Spray an 8 x 8 casserole dish with cooking spray.
Spread chicken evenly along bottom of baking dish and top with the ham. Then layer the cheese slices on top of ham.
Sauce: Melt butter in small sauce pan over medium heat. Quickly stir in flour, and mix until just combined, about 30 seconds. Slowly pour in the milk while continuously whisking. continue to whisk constantly until sauce begins to thicken.
Add in lemon juice, mustard, paprika, salt and pepper and stir well. Bring sauce to a low simmer while still whisking. Simmer until thickened, about 2-3 minutes. If sauce becomes too thick, thin it with a bit of broth. Remove from heat and pour over casserole.
In a small bowl, combine Panko and dried parsley (and additional salt and pepper if desired) and then sprinkle mixture evenly over top of casserole. Lightly mist Panko with nonfat cooking spray.
Place in oven and bake uncovered for about 30 minutes or until top of casserole has turned light brown, and the casserole is hot and bubbly throughout.