Preheat your oven to 350°F (175°C). Lightly grease a 9x13 inch baking dish.
Without separating the rolls, use a large serrated knife to slice the entire slab of rolls in half horizontally. Place the bottom half in the prepared baking dish.
Layer the ham evenly over the bottom slab of rolls, followed by an even layer of the Swiss cheese.
Place the top half of the rolls over the cheese to complete the sandwiches.
In a small bowl, melt the butter. Whisk in the Dijon mustard, poppy seeds, dried onion, and Worcestershire sauce until combined.
Slowly pour the butter mixture over the top of the rolls. Use a brush or spatula to spread it evenly, making sure some drips down the sides.
Cover the dish with foil and bake for 20 minutes, or until the cheese is fully melted and the sliders are heated through.
Remove the foil and bake for another 3 to 5 minutes, until the tops are golden brown. Watch them closely to prevent burning.
Let the sliders rest for a minute before slicing them apart. Serve warm.