Spread the chopped onion over the bottom of the slow cooker. Place the chicken on top of the onion.
In a medium bowl, whisk together the ketchup, vinegar, mustard, molasses, onion powder, cumin, garlic powder, hot sauce, and salt. Pour the sauce over the chicken.
Cover the slow cooker and cook on low for about 5 to 6 hours, until the chicken is fork-tender and cooked through.
Remove chicken and shred it. Then return it to the slow cooker and stir until coated with sauce. Serve with rolls or buns for a delicious sandwich!
Notes
If you don't have molasses, you can try using honey, dark corn syrup, maple syrup, or dark brown sugar instead. I haven't tried this recipe with substitutions though, so I can't vouch for the results. :)