Preheat oven to 375°F (190°C). Lightly grease a baking dish or line it with parchment paper.
Slice the rolls in half horizontally as a whole slab, keeping the tops and bottoms connected. Place the bottom half in the prepared baking dish.
Layer the ham evenly over the bottom rolls, followed by the Swiss cheese slices. Cover with the top halves of the rolls.
Make the glaze: In a small bowl, mix melted butter, Dijon mustard, relish (if using), salt, and pepper.
Brush the glaze generously over the tops of the rolls. Sprinkle with poppy seeds if desired.
Cover with foil and bake for 15–18 minutes, until the cheese is melted and the sandwiches are heated through.
Uncover and bake an additional 3–5 minutes until the tops are golden and slightly crisp.
Let rest for 5 minutes, then slice and serve warm. Perfect for parties, picnics, or game day!