Step 1: Preheat your oven to 350°F (175°C). Lightly grease a 9x13 inch baking dish.
Step 2: Carefully slice the entire slab of Hawaiian sweet rolls horizontally, keeping them connected at the edges if possible. Place the bottom layer of rolls into your prepared baking dish.
Step 3: Arrange half of the ham slices evenly over the bottom layer of rolls.
Step 4: Place a single layer of Swiss cheese slices over the ham.
Step 5: Add the remaining ham slices on top of the cheese, then top with the remaining Swiss cheese slices.
Step 6: Gently place the top layer of Hawaiian rolls back onto the ham and cheese stack. Press down lightly.
Step 7: In a small microwave-safe bowl or saucepan, melt the unsalted butter. Stir in the Dijon mustard, Worcestershire sauce, garlic powder, and dried minced onion until well combined.
Step 8: Evenly pour the butter mixture over the top of the assembled sliders. Use a pastry brush to ensure every roll is coated. If desired, sprinkle with poppy seeds.
Step 9: Cover the baking dish tightly with aluminum foil. Bake for 15 minutes.
Step 10: Remove the foil and continue baking for another 5-10 minutes, or until the tops are golden brown and the cheese is bubbly and completely melted.
Step 11: Remove from the oven and let the sliders rest for a few minutes.
Step 12: Use a serrated knife to cut along the original score marks of the Hawaiian rolls to separate them into individual sliders. Serve immediately.