Set the oven to 375°F (190°C) and lightly grease a 9-inch square baking dish.
Separate the refrigerated biscuits and gently flatten each one into a circle about 4 inches wide.
Place a portion of ham and one slice of Swiss cheese in the center of each flattened biscuit. Fold the dough around the filling and pinch the edges firmly to seal.
Place the filled biscuits seam-side down in the prepared dish.
In a small bowl, combine the melted butter, Dijon mustard, Worcestershire sauce, and onion powder. Stir until everything is well blended.
Generously brush the butter mixture over the tops of the biscuits, then sprinkle with poppy seeds.
Bake for 18–22 minutes, or until the biscuits are puffed and golden brown and the cheese has melted.
Allow the sliders to rest for about 5 minutes before serving warm.
