In a small bowl, mix the mayonnaise and Dijon mustard. Spread the mixture evenly on the cut sides of the rolls.
Layer the roast beef and Swiss cheese on the bottom half of each roll. Cover with the top half of the rolls.
Place sliders on a baking sheet. In a separate small bowl, combine the melted butter, Worcestershire sauce, poppy seeds, and garlic powder. Pour evenly over the sliders.
Cover with aluminum foil and bake in the preheated oven for 20 minutes, then uncover and bake for another 5 minutes or until the tops are golden brown.
Notes
Feel free to add caramelized onions or fresh arugula for more flavor!