Begin by placing the boneless chicken breasts between two layers of plastic wrap, then gently pound them to a uniform thickness of 1/4 to 1/2 inch. Season both sides generously with salt and pepper.

Create a breading station by arranging three shallow bowls in a line. Fill the first with all-purpose flour, the second with beaten eggs, and the third with Panko breadcrumbs.

Dredge a pounded chicken breast in the flour, then dip it into the beaten eggs, and finally coat it with Panko breadcrumbs. Repeat for each chicken breast.

Preheat your oven to 400°F (200°C) and heat a large skillet over medium heat with olive oil or butter. Add the breaded chicken breasts and pan-fry for 3 minutes on each side until golden brown.

Layer a slice of ham and cheese over each chicken breast and transfer the skillet to the preheated oven. Bake for 15 to 20 minutes until the cheese melts and the chicken's internal temperature is 165°F (75°C).

While the chicken is baking, combine mayonnaise, Dijon mustard, honey, lemon juice, and Worcestershire sauce in a bowl. Whisk together until smooth and adjust seasoning with salt and pepper.

Remove the chicken from the oven, serve drizzled with the creamy mustard sauce, and garnish with freshly chopped parsley if desired.