On a rimmed baking sheet place bottom half of dinner rolls and top with 2 folded slices of ham and 1 slice of swiss cheese. Spread about 1 tsp of mayonnaise on each top-half of roll and place on top of ham and cheese. You want the rolls to be snug together, kissing just a bit so the sauce can soak up into all of the nooks and crannies.
In a small bowl combine the mustard, melted butter, onion powder, Worcestershire sauce, poppy seeds, and brown sugar. Mix until combined and evenly pour over the assembled rolls. Cover with foil and refrigerate until ready to bake.
Preheat oven to 400 degrees.Bake covered with foil for 10 minutes, remove the foil and bake for an additional 5-10 minutes or until the tops are browned, and cheese is good and melted.