Preheat the oven to 350 degrees.
Halve the rolls horizontally.
Line a 9x13 inch baking dish with the roll bottoms.
Layer the ham and cheese over the roll bottoms.
Combine the butter, Worcestershire sauce, mustard, poppy seeds and onion in a bowl and mix well.
Drizzle half the butter mixture over the ham.
Cover with the roll tops.
Drizzle the remaining butter mixture over the tops.
Bake for 10 minutes.