Step 1: Preheat oven to 350°F and lightly grease a 9x13 inch baking dish.
Step 2: Slice the entire block of Hawaiian rolls in half horizontally keeping them connected and place the bottom half in the baking dish.
Step 3: Layer the deli ham evenly across the bottom half of the rolls then top with Swiss cheese slices.
Step 4: Place the top half of the rolls over the cheese.
Step 5: In a small bowl melt butter and whisk in Dijon mustard, Worcestershire sauce, poppy seeds, onion powder, and brown sugar until combined.
Step 6: Pour the butter sauce evenly over the tops of the rolls and let rest for 10 minutes.
Step 7: Cover the dish tightly with aluminum foil and bake for 15 minutes.
Step 8: Remove foil and bake for an additional 5 to 10 minutes until the tops are golden brown and cheese is melted.
Step 9: Let cool for 2 to 3 minutes then slice along the natural seams and serve warm.