Pre-heat the oven to 350 degrees F.
Slice the Hawaiian rolls in half. Place the roll bottoms into two 13x9 baking pans.
Layer one slice of ham on each roll bottom. Fold the Swiss cheese slices into quarters. Place two quarters on each roll. Place the tops on the rolls.
Place the butter in a microwave-safe container. Heat it in 25-30 second increments, stirring in between each increment until the butter is melted.
Add the Dijon mustard, Worcestershire sauce, brown sugar, poppy seeds, and onion powder to the butter. Stir to combine.
Pour the butter mixture evenly over the rolls.
Cover the pans with aluminum foil. Bake for 10 minutes. Remove the foil. Bake for another 3 minutes or until heated through and the cheese is melted.