Preheat the oven to 400°F.
Lightly coat a 9 x 5-inch loaf pan with cooking spray.
Place the ground chicken in a large mixing bowl.
Add the egg, mayonnaise, plain breadcrumbs, minced onion, garlic powder, dried parsley, salt, and ground black pepper.
Mix until the ingredients are evenly combined. Do not overmix.
Transfer half of the chicken mixture to the prepared loaf pan.
Spread the mixture evenly across the bottom of the pan.
Layer 3 slices of Virginia ham over the chicken mixture.
Place 3 slices of Swiss cheese over the ham.
Repeat with the remaining 3 slices of Virginia ham and 3 slices of Swiss cheese.
Add the remaining chicken mixture over the ham and cheese layers.
Spread the chicken mixture evenly over the top and gently seal the edges.
Place the loaf pan in the preheated oven.
Bake for 25 minutes.
Carefully remove the meatloaf from the oven.
Sprinkle the fresh breadcrumbs or panko breadcrumbs evenly over the top.
Return the meatloaf to the oven.
Bake for an additional 15 minutes, or until the meatloaf is fully cooked and the topping is lightly golden.
If the breadcrumbs begin to brown too quickly, loosely cover the loaf pan with foil during the remaining baking time.
While the meatloaf finishes baking, prepare the creamy Dijon gravy.
Place the butter in a saucepan over medium heat.
Once the butter has melted, whisk in the flour.
Cook the butter and flour mixture for 1 minute, whisking constantly.
Add the heavy cream, milk, Worcestershire sauce, and Dijon mustard.
Whisk until the sauce is smooth and fully combined.
Allow the sauce to come to a gentle simmer.
Cook for 3 to 4 minutes, or until the gravy thickens.
Add the grated parmesan cheese and freshly grated nutmeg.
Whisk until the parmesan cheese is melted and the gravy is smooth.
Taste the gravy and season with salt and ground black pepper as needed.
Remove the meatloaf from the oven.
Allow the meatloaf to rest in the loaf pan for 10 minutes.
Carefully lift or remove the meatloaf from the pan.
Slice the meatloaf into portions.
Serve warm with the creamy Dijon gravy on the side or spooned over the top.