Combine all spices in a small bowl. Reserve 1 tsp of mix for BBQ sauce.
Place chicken in slow cooker. Sprinkle the spice mix over the chicken.
Cover and cook on high for 3-4 hours. Once done cooking, use two forks, a hand mixer or stand mixer to shred the meat. Set aside and keep warm.
For the Cranberry BBQ sauce
Saute the onion in about 1 Tbsp olive oil until softened, about 3-4 minutes. Add whole cranberry sauce, apple cider vinegar, Worcestershire sauce, mustard, ketchup and 1 tsp reserved spice mix. Cook for about 5 minutes till thickened and bubbling.
Remove chicken from slow cooker and top with BBQ sauce.
Using a programmable slow cooker prevents the over cooking of boneless skinless chicken breasts but you'll want to make sure you don't discard the cooking juices from the slow cooker.Another option is to use chicken thighs instead of chicken breasts which are much harder to overcook due to the extra fat in the meat.For easiest shredding of the chicken, use a hand mixer or stand mixer while the meat is still hot.If you want to make this in the pressure cooker, add 1 cup of chicken stock with the chicken and cook for 9 minutes on high pressure.