Pat the chuck roast dry and season both sides with salt, pepper, garlic powder, and smoked paprika. Add the olive oil to a pan and turn the heat to medium high. Sear each side for 2 minutes.
Add sliced onions to the bottom of the crock pot. Place the seared chuck roast on top.
In a bowl, combine BBQ sauce, beef broth, apple cider vinegar, and brown sugar. Pour over the roast.
Cover and cook on LOW for 8 hours or HIGH for 4-5 hours, until the meat is fork-tender and easy to shred.
Remove the roast and shred it with two forks, discarding any fat. Skim excess fat from the juices, then return the meat to the sauce in the slow cooker to stay warm.
Preheat the oven to 350 degrees F. Place the buns on a sheet pan lined with parchment paper.
Split the slider buns. Add pickles, followed by the shredded beef, cheddar cheese and fried onions (if using). Add the top buns back on. Mix the melted butter and garlic salt together and brush over the tops of the slider buns.
Pop into the oven for 10 minutes until the buns are golden brown and the cheese is melted.
Cut the sliders and serve with a side of oven fries or potato chips and dig in!