Preheat the oven to 350°F.
Slice the whole sheet of Hawaiian rolls in half, keeping the rolls attached to each other. Set the top half of the rolls aside.
Place the rolls in a 9x13 glass baking dish.
Spread mayonnaise over the rolls.
Top with a generous layer of overlapping slices of cheddar cheese.
Mound roast beef over the cheese layer.
Top with another generous layer of cheddar cheese.
Place the tops of the rolls over the prepared sliders.
Whisk together melted butter, mustard, barbecue sauce, and poppy seeds.
Drizzle butter mixture over the rolls and use a pastry brush to spread the mixture over the tops of all of the rolls.
Cover the baking dish with aluminum foil and bake for 30 minutes. Remove the aluminum foil and cook for about 5 minutes longer or until the tops of the rolls are toasted and golden brown.