Preheat and Prep: Preheat your oven to 375°F (190°C). Line a 9x13 inch baking pan with aluminum foil and spray generously with non stick cooking spray. Set aside.
Slice the Rolls: Using a large serrated knife, carefully slice the entire connected slab of Hawaiian rolls in half horizontally. You should have one connected "slab" of tops and one "slab" of bottoms. Place the bottom slab in the prepared pan.
Prepare the Chicken: In a medium bowl, combine the cooked, shredded chicken and the ranch dressing. Stir until the chicken is evenly coated.
Assemble the Sliders: Spread the ranch chicken mixture evenly over the bottom slab of rolls. Layer the sliced Swiss cheese over the chicken, covering it as evenly as possible. Place the top slab of rolls over the cheese.
Make the Topping: In a medium microwave safe bowl, melt the butter (about 1 minute on high). Add the Dijon mustard, poppy seeds, dried minced onion, Worcestershire sauce, salt, and pepper. Whisk until well combined.
Pour and Rest: Slowly and evenly pour the butter mixture over the top slab of rolls, using a spatula to spread it if needed. Cover the pan with aluminum foil and let it sit at room temperature for 5-10 minutes.
Bake Covered: Bake, covered with the foil, for about 16 minutes, or until the cheese is melted.
Bake Uncovered: Remove the foil and bake for another 4-5 minutes, until the tops are golden brown. Watch closely to prevent burning.
Serve: Let the sliders cool for a few minutes in the pan. Use a sharp knife to slice between the rolls into individual sliders. Serve warm and enjoy!