In a small bowl, whisk together the ketchup, brown sugar, apple cider vinegar, chili powder, salt, garlic powder, onion powder, and paprika. Pour about half of the sauce into the base of your slow cooker.
Place the chicken in the slow cooker, add the sliced onions, and cover with the rest of the sauce. Cook on low for 3 hours.
At the end of the three hours, shred the chicken, and serve on buns.
Notes
It's best if you know your slow cooker. Mine tends to cook things faster than most recipes call for. If yours does as well, then you will be good with the time listed here. If yours does not, you may want to add an hour.Resist the urge to peek, your slow cooker needs to stay closed to cook most effectively!