Preheat your oven to 375°F. Take a 9×13-inch baking dish and spray it with nonstick cooking spray.
Pour the beef broth into a large skillet and heat it over medium heat until it begins to simmer, about 5 minutes.
Add the deli sliced roast beef to the simmering broth and stir gently until the beef is warmed through, about 2 minutes.
Place the bottom halves of the Hawaiian rolls in the prepared baking dish with cut sides facing up.
Top the rolls with 6 slices of provolone cheese.
Spoon the warmed roast beef over the cheese layer, allowing any excess broth to drip off.
Place the remaining 6 slices of provolone cheese on top of the roast beef.
Carefully place the top halves of the rolls over the cheese.
In a small bowl, blend the melted butter, dijon mustard, dried onion flakes, and garlic powder together.
Generously brush the butter sauce all over the tops of the rolls.
Cover the baking dish with nonstick foil and bake in the oven for 20 minutes.
Remove the foil and bake for an additional 5 minutes to brown the tops.
Carefully cut the sliders into individual portions. Serve them warm.