Preheat the oven to 350°F.
Slice the Hawaiian rolls in half horizontally, keeping the top and bottom halves intact.
Place the bottom half of the rolls in a 9x13-inch baking dish.
If using, spread a thin layer of mayonnaise on the bottom rolls.
Layer all the sliced ham evenly over the bottom half of the rolls.
Add a layer of Swiss cheese over the ham.
If using, spread Dijon mustard on the inside of the top half of the rolls.
Place the top half of the rolls over the cheese to form a sandwich slab.
In a small bowl, whisk together the melted butter, Dijon mustard, poppy seeds, onion powder, and garlic powder.
Pour the butter mixture evenly over the tops of the rolls, spreading it gently to coat.
Cover the baking dish loosely with foil.
Bake for 15 minutes, then remove the foil and bake uncovered for 5 more minutes or until the tops are golden.
Remove from oven and let sit for 5 minutes before slicing into individual sliders.
Serve warm.