Put the chuck roast in a slow cooker with the taco seasoning, chopped onion, and beef stock. Cover and cook on HIGH for 4 to 5 hours, or until the beef is very tender. Alternatively, cook the beef in a large Dutch oven or saucepan on the stovetop — you might need extra liquid — over low heat until very tender, about 2 hours.
Remove the beef and chop or shred. Refrigerate until you are ready to assemble the sliders and bake.
Sliders And Baking
Heat the oven to 375 F.
Spray a large sheet of heavy duty foil — large enough to wrap the rolls — with nonstick cooking spray.
Slice the rolls in half horizontally. Place the bottom rolls in the center of the prepared foil. Separate the bottoms but keep them close together.
Spread sour cream over the bottoms and then sprinkle with cilantro, if using.
Top the sour cream layer with the cooked chopped or shredded beef.
Drizzle 4 to 5 tablespoons of taco sauce over the beef layer and then top with the chopped red onion.
Top with sliced pickled chile pepper rings.
Overlap the cheese slices over the chile pepper layer.
Place the top of the rolls over the cheese. If desired, separate the tops slightly or wait until they come out of the oven.
Combine the melted butter with the remaining 1 tablespoon of taco sauce, 1/4 teaspoon of garlic powder, and 1/4 teaspoon of chili powder. Brush the mixture over the tops of the rolls.
Wrap the foil over the top; seal the top and ends. Place the foil package on a baking sheet.
Bake in the preheated oven for 20 minutes. Uncover the tops and bake for 5 minutes longer to brown slightly.
Remove from the oven and carefully cut and separate to make individual sliders.