Preheat oven to 350°F and grease a 9x13-inch pan with cooking spray. Cut the buns down the middle. Arrange the bottom of the buns in the baking dish, and set aside the tops.
In a small bowl, combine mayo, garlic powder, onion powder, mustard and Worcestershire sauce. Coat the bottom half of the buns with the spread.
Now assemble the sliders, layering with roughly 3 slices of roast beef, 1 slice of cheese (cut in half and criss-crossed over the meat), and a sprinkling of french fried onions. Put the top halves of the buns back on, brush the tops with melted butter, and sprinkle with sesame seeds. Note: If you have extorter butter, feel free to brush the sides of the buns as well!
Bake roast beef sliders on Hawaiian rolls for 12-15 minutes or until the tops are golden brown.
Meanwhile, prepare the au jus dipping sauce as per the instructions on the packet (usually mixing it with water and heating in a saucepan or microwave). Serve sliders with a side of warm au jus sauce for dipping.
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Notes
If using King's Hawaiian roll, you can keep individual rolls connected when prepping the sliders and simply use a large serrated knife to slice slab of rolls through the center. After roast beef sliders have been baked, simply cut them into individual sandwiches
To avoid soggy sliders, make sure that Hawaiian rolls are evenly sliced between the top and bottom.
If slices of cheese are too large for sliders, simply break slices in half and then criss-cross them over the meat when assembling sliders.
Don't overcook sliders. If you see the buns turning too brown too fast, cover the sliders with aluminum foil and bake them until the cheese is fully melted.
Adjust sesame seeds as desired, using as much or as little as you'd like.
Let sliders cool a few minutes before slicing so that sliders can settle and be less likely to fall apart.