Slice rolls in half, keeping tops and bottoms together.
Melt butter and whisk in onion, mustard, poppy seeds and Worcestershire sauce.
Brush the mixture evenly on both the top and bottom half of the rolls.
On the bottom half of each roll, top the mustard mixture a small slice of swiss cheese and a slice of ham. You will need to fold the ham over so it's not hanging over the edge of the roll.
Cover with foil and bake about 15-20 minutes, or until cheese is melted.
Remove from oven, separate rolls and serve.
Notes
Make sure to cover with foil when baking so the rolls don't get too brown on top.