Preheat oven to 350.
Grease a 9x13-inch baking dish.
Combine butter, mustard, Worcestershire sauce, brown sugar, poppy seeds, and dried onion.
Slice the rolls to make sandwiches. Remove tops and set aside.
Place the bottom pieces into the prepared baking dish.
Layer the ham onto the rolls.
Top the ham with the Swiss cheese.
Place the tops of the rolls onto the sandwiches.
Brush or pour the liquid mixture evenly over the rolls.
Bake 20 minutes or until the rolls are lightly browned and cheese has melted.
Separate into individual sandwiches to serve.