Preheat oven to 350°F and butter a 9x13" baking dish.
Slice Hawaiian rolls in half horizontally using a large bread knife. Make sure to keep the rolls connected to each other while cutting. Once sliced, remove the top section and place on a cutting board.
Add bottom section to your baking dish. Spread mayo onto the insides of both the bottom and top sections. Then place a slice of ham and cheese on each roll in the bottom section. Add top roll section back to baking dish and evenly match up.
In a small bowl, whisk together the butter, mustard, Worcestershire sauce, onion powder and poppy seeds. Pour evenly over all of the rolls. Let sit about 10 minutes for sauce to soak in.
Cover ham sliders with foil and bake for 10-15 minutes. Uncover and cook an additional 2 minutes to brown the top of the rolls. Best served while warm.
Another fun way to make these is to put the poppyseed sauce in the inside, wrap with foil and place on the grill until melted, about 5 minutes.