Preheat the oven to 400°F (200°C).
In a large bowl, mix ground chicken with minced onion, garlic powder, dried parsley, egg, mayonnaise, plain breadcrumbs, salt, and pepper.
Grease a loaf pan and press half of the chicken mixture into the bottom.
Layer the ham slices and Swiss cheese over the chicken mixture.
Cover with the remaining chicken mixture and press down.
Bake for 25 minutes.
Remove from the oven, sprinkle with panko breadcrumbs, and bake for an additional 15 minutes.
In a saucepan, melt butter, whisk in flour, and slowly add milk and cream to make a gravy. Add Worcestershire sauce, Dijon mustard, Parmesan, nutmeg, salt, and pepper. Simmer until thickened.
Let the meatloaf rest for 10 minutes before slicing. Serve with the prepared gravy.