Preheat oven to 350 degrees F. Prepare a large baking sheet lined with aluminum foil.
Halve dinner rolls and place 1 slice each of ham and Swiss inside each roll. Place rolls very close together on the baking sheet.
In a medium bowl, whisk together melted butter, onion flakes, mustard, Worcestershire sauce, and poppy seeds. Pour evenly over all of the sandwiches. Let sit 10 minutes or until butter sets slightly. Cover with foil and bake for 15 minutes, or until cheese is melted.
Uncover and cook for 3-4 additional minutes, or until tops are slightly brown and crispy. Serve warm.
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