Heat the oven to 350°F and line a 9-by-13-inch pan with parchment. Slice the connected Hawaiian rolls horizontally and place the bottoms in the pan.
Spread mustard thinly over the bottoms. Layer half the cheddar, folded roast beef, dry pepper strips and remaining cheddar over the bread.
Replace the tops and brush with butter mixed with garlic powder. Cover loosely with foil.
Bake for 15 minutes, then uncover and bake for 8 to 10 minutes until the cheese melts and the center reaches 165°F.
Rest for 5 minutes and cut into 12 sliders with a serrated knife.