Preheat oven to 350°F (175°C).
Slice the slider buns in half and place the bottom halves in a baking dish.
Spread a layer of mayonnaise and Dijon mustard on the bottom buns.
Layer the roast beef evenly over the buns, followed by the cheddar cheese slices.
Place the top halves of the buns over the cheese.
In a small bowl, mix melted butter, Worcestershire sauce, poppy seeds, minced onion, garlic powder, salt, and pepper.
Brush the butter mixture over the top of the sliders.
Cover with foil and bake for 15 minutes.
Remove the foil and bake for another 5 minutes until golden brown.
Serve warm and enjoy!