Preheat the oven to 350 degrees F (175 degrees C). Line a 9-inch square baking pan with aluminum foil and spray with cooking spray.
Pull attached rolls from the package. Use a serrated knife to cut through horizontally, separating rolls into a top and bottom "slab."
Place bottom slab into the prepared pan. Layer with 1/2 of the ham, all of the Swiss cheese, followed by remaining ham. Cover with top slab.
Whisk melted butter, mustard, poppy seeds, Worcestershire sauce, onion, salt, and pepper together in a small bowl until well combined.
Slowly pour butter mixture over all rolls. Use a spatula to spread it evenly; some will pool at the bottom. Cover with aluminum foil and let stand at room temperature for 5 to 10 minutes.
Bake, covered, in the preheated oven until cheese has melted, about 20 minutes. Uncover and continue baking until rolls are browned, 3 to 5 more minutes. Cut to separate sliders.