Preheat the oven to 325° F.
Tightly wrap the leftover brisket in tin foil. Optional: Add 1 cup broth before wrapping.
Heat in the oven for 10-15 minutes or until the internal temperature of the brisket is 160° F.
Shred the cabbage in a bowl.
Finely chop the scallions and combine them with the cabbage.
Combine the olive oil, honey, apple cider vinegar, Dijon mustard, salt, and pepper in a small bowl. Whisk the ingredients to make a dressing.
Pour the dressing over the cabbage.
Meanwhile, preheat a large cast iron skillet on medium heat. Melt the butter in the preheated skillet.
Sauté the onions for around 5 minutes until they are caramelized.
Combine the garlic and the onions and continue to cook for an additional minute.
Add the reheated brisket, Worcestershire, paprika, salt, and pepper to the skillet. Heat on low heat for around 1 minute until everything is combined.
Place the bottom half of the potato buns on the baking sheet.