Preheat oven to 350°F. Line a 9×13-inch baking dish with foil.
Whisk melted butter, Dijon, Worcestershire, brown sugar, poppy seeds, onion powder, garlic powder, salt, and pepper.
Slice the slab of rolls in half horizontally. Place the bottoms in the lined dish.
Spread mayonnaise over the cut sides. Layer ham and Swiss over the bottoms, then cap with the roll tops.
Spoon the butter mixture evenly over the tops and down the sides. Let soak for 5–10 minutes.
Cover tightly with foil and bake 18–20 minutes until hot and the cheese is melted.
Uncover and bake 3–5 minutes more to lightly toast the tops.
Rest 5 minutes, scatter parsley, then separate the sliders and serve warm.