Do the prep. Preheat the oven to 325°F or 163°C. Lightly grease a 9×13 inch baking dish.
Assemble the sliders. Cut the Hawaiian rolls in half, removing the top and placing the bottom of the rolls into the baking sheet. Stack the ham, Swiss, and pickles evenly over the rolls in the pan. Cover with the roll tops.
Make the Dijon sauce. In a small bowl, whisk together melted butter and Dijon mustard. Stir in the minced onion. Using a spoon, pour the Dijon mustard mixture over the sliders.
Bake. Cover the baking dish with aluminum foil. Place into the oven and bake for 15 minutes. Remove the foil and bake for 10 minutes more, or until the rolls are a toasted brown. Serve hot.