Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
Slice the slider buns in half horizontally. Place the bottom halves of the buns on the prepared baking sheet.
Spread mayonnaise on the bottom halves of the buns.
Layer the roast beef evenly over the buns, then top with the provolone cheese slices.
Place the top halves of the buns on the cheese.
In a mixing bowl, whisk together the melted butter, Dijon mustard, Worcestershire sauce, dried minced onion, and poppy seeds.
Use a pastry brush to generously brush the sauce over the tops of the sliders.
Cover the sliders loosely with aluminum foil and bake in the preheated oven for 10 minutes.
Remove the foil and bake for an additional 5-10 minutes, or until the cheese is melted and the tops are golden brown.
Remove the sliders from the oven and let them cool for a few minutes before serving.