Cut slider buns in half and place the bottoms in a greased casserole dish.
Mix together mayo and Dijon mustard then spread over the bottom buns.
Place the ham on the slider buns, overlapping the pieces.
Place the Swiss cheese on the ham, and then place the tops of the slider buns.
In a small bowl, combine melted butter, onion powder, Worcestershire sauce, and poppy seeds.
Pour the butter mixture over the sliders and cover the casserole dish with aluminum foil. Bake for 10 minutes, then remove the foil and continue baking for 10 more minutes, or until the cheese melts.
Remove from the oven. Use a sharp knife to cut the sliders apart. Serve warm and enjoy!