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.
Notes
Variation: Add a layer of thinly sliced dill pickles or a swipe of honey mustard for extra zip. To serve a crowd, assemble several pans ahead, cover, and refrigerate up to 24 hours; add 3–5 minutes to the bake time from cold. Leftovers reheat well wrapped in foil at 325°F for 10 minutes.This recipe is an original creation inspired by classic Hawaiian Baked Ham and Swiss Sandwiches flavors. All ingredient ratios and instructions are independently developed.