Heat the oven and prep the pan: Heat the oven to 350°F and lightly grease a 9x13-inch baking dish.
Split the rolls: Using a long serrated knife, slice the entire slab of rolls in half horizontally in one steady sawing motion. Keep the rolls connected to each other. Set the bottom slab in the baking dish.
Layer the ham and cheese: Lay half the Swiss slices over the bottom slab, then arrange the ham on top, folding each slice into loose ruffles as you go. Cover the ham with the remaining Swiss and set the top slab of rolls back on.
Mix the butter glaze: Whisk together the melted butter, Dijon, poppy seeds, dried minced onion, Worcestershire sauce, and garlic powder until it looks evenly speckled.
Brush and soak: Spoon the butter mixture slowly over the tops, working it into the seams between the rolls. Let the pan sit for a few minutes while the oven finishes heating so the glaze soaks in instead of running off.
Bake covered: Cover the dish with foil and bake for 15 minutes, until the cheese has melted through the middle.
Bake uncovered: Uncover and bake 5-8 minutes more, until the tops are golden and glossy. Deli ham is already fully cooked, so bake until the centers reach 165°F.
Cut and serve: Sprinkle with parsley, cut down through the seams with a sharp knife, and serve warm.
Notes
Slice the rolls as one connected slab instead of separating them, so the cheese melts into the seams and the sliders stay together in the pan. Deli ham is fully cooked; bake until the centers reach 165°F.