Preheat the Oven:**
- Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or lightly grease it.
**Prepare the Dough:**
- On a lightly floured surface, roll out the pizza dough into a large rectangle, approximately 12x14 inches.
**Assemble the Stromboli:**
- In a small bowl, mix together the Dijon mustard and mayonnaise (if using). Spread this mixture evenly over the dough, leaving about 1 inch of space around the edges.
- Layer the Swiss cheese slices down the center of the dough, followed by the deli ham slices.
- Evenly distribute the cooked chicken breast over the ham.
- Carefully fold the sides of the dough over the filling, then roll the dough tightly from one long edge to the other, creating a log shape. Pinch the seams and ends to seal the Stromboli.
**Add Toppings:**
- Place the Stromboli seam-side down on the prepared baking sheet.
- Brush the top of the Stromboli with melted butter, then sprinkle it with garlic powder, dried parsley, and grated Parmesan cheese.
**Bake the Stromboli:**
- Bake the Stromboli in the preheated oven for 25-30 minutes, or until the crust is golden brown and crispy.
- Remove the Stromboli from the oven and let it rest for about 5 minutes before slicing.
**Serve:**
- Slice the Chicken Cordon Bleu Stromboli into pieces and serve warm. Pair it with a simple green salad or a dipping sauce like honey mustard or marinara.