Preheat oven to 350°F and lightly grease a 9 × 13-inch baking dish. Keep the rolls connected and use a serrated knife to slice horizontally through the entire slab, creating one top and one bottom layer. Place the bottom half cut-side up in the baking dish.
Mix mayonnaise with 1 tablespoon Dijon mustard. Spread evenly over the bottom rolls, reaching all the way to the edges.
Loosely fold the ham slices and distribute them evenly over the rolls. Top with overlapping Swiss cheese slices, trimming them as needed for even coverage. Sprinkle with black pepper.
Place the connected top half of the rolls over the cheese and gently press into place without flattening the rolls.
Whisk melted butter, 1 tablespoon Dijon, Worcestershire sauce, poppy seeds, onion powder, garlic powder, and honey, if using. Brush or spoon evenly over the tops, allowing a little mixture to run between the rolls. Sprinkle with Parmesan.
Loosely tent the baking dish with foil and bake on the center rack for 15 minutes, until the filling is hot and the cheese has started melting.
Remove the foil and bake uncovered for another 7–10 minutes, until the cheese is completely melted and the tops are glossy and golden brown.
Rest for 5 minutes, then cut along the natural seams with a sharp knife. Serve warm.