Preheat the oven to 360 degrees and then line a 9 x 13 inch baking pan with foil and spray some non-stick cooking spray and leave it aside. Disposable aluminum pan would be easy to clean and transport.
Remove the rolls from the package and slide out the tray. Slice them into half with the tops in one sheet and the bottoms on the other sheet.
Layer the roast beef on the rolls and then add the cheese. Top with the sheet of the tops and set aside.
Melt the butter in a small microwave safe bowl for about a minute. Add in the Worcestershire sauce, mustard, poppy seeds, onion, salt and pepper. Nicely pour this over the top of the rolls. Cover it with foil and allow it to rest for a minimum of 10 minutes.
Bake it covered for 20 minutes. Remove it from the foil and bake it for another 5 to 8 minutes.