In a large bowl, stir together chicken, celery, buffalo sauce, and Ranch seasoning powder. Add the cream cheese and stir until everything is completely combined.
Place the bottom half of the rolls in a greased 12 x 8-inch or 11 x 7-inch baking dish. Spread the chicken mixture over top. Add a layer of shredded cheese. Place the top half of the rolls on top.
In a small bowl or large measuring cup, whisk together warm melted butter, brown sugar, Worcestershire sauce, garlic powder, and onion powder. Drizzle the sauce onto the rolls, sprinkle with poppy seeds and sesame seeds (if desired), and cover with foil.
Bake until the cheese is melted, about 20 minutes. Uncover and bake until the tops are lightly browned, about 3-5 more minutes. Serve warm.
Notes
Instead of spreading all of the rolls with the meat filling at once, you can separate the individual rolls and spread the filling on them one at a time.
If you want to be able to lift all of the sliders out of the pan so that you can transfer them to a serving board, line your baking dish with parchment paper. Let some of the parchment hang over the edges of the pan (like handles), and then just lift out the entire tray of sandwiches when they’re done baking. Your guests can pull them apart, or you can cut through them with a knife.
For even more flavor, add some herbs to the butter mixture. For instance, dried parsley, basil, chives, or oregano would be delicious. You can also garnish the finished sliders with sliced green onions or chopped fresh parsley.