Cut the Hawaiian rolls in half horizontally. Place the bottom halves in a baking dish.
Layer the ham and Swiss cheese on the rolls. Place the top halves of the rolls on top.
In a small bowl, mix together the melted butter, Dijon mustard, Worcestershire sauce, poppy seeds, and onion powder.
Pour the butter mixture evenly over the sandwiches.
Cover the baking dish with aluminum foil and bake for 15 minutes. Remove the foil and bake for an additional 5 minutes, or until the tops are lightly browned and crispy.
Remove from the oven and let cool slightly before serving.