Heat the vegetable oil in a skillet over medium heat. Add the roast beef slices and cook until heated through, about 2-3 minutes.Make sure to stir it from time to time until it is fully heated.
In a small pot on the stove over medium-low head, add the cheese, milk, and black pepper and stir continuously until fully melted.
7 slices American cheese slices, sprinkle black pepper, 1/4 cup milk
Make the Sauce
In a medium bowl stir together all of the ingredients to make the Arby's sauce.
1/4 cup barbecue sauce, 1 tablespoon ketchup, 1/2 teaspoon onion powder, 1/2 teaspoon garlic powder, 1/2 teaspoon apple cider vinegar
Build the Sandwiches
Heat up the buns in whatever method you prefer. Slice them in half if they aren't already.
To assemble the sandwiches, Spread some sauce on the top and bottom of the bun, place a pile of roast beef on the bottom piece, top with melted cheese sauce, and top with the top bun.
4 onion hamburger buns
Serve the sandwiches immediately. Enjoy your homemade Arby's Beef and Cheddar with a side salad or with some curly fries.