Preheat oven to 350°F (175°C).
Place bottom halves of the rolls in a baking dish.
Layer each roll with a slice of ham and a slice of cheese.
Put the tops of the rolls back on and set aside.
In a small bowl, combine melted butter, Dijon mustard, Worcestershire sauce, poppy seeds, and minced onion.
Pour the mixture over the sandwiches, distributing evenly.
Cover the baking dish with aluminum foil and bake for 15 minutes.
Remove the foil and bake for an additional 5 minutes to toast the tops.