In a small bowl, combine the salt, mustard powder, chili powder, cumin, onion powder, black pepper, garlic powder, and paprika. Stir to mix and set aside.
Spray the slow cooker with nonstick cooking spray. Place the chicken breasts in bowl.
Cover each chicken breast liberally with the seasoning mix.
Cook the chicken breasts on low for 6 hours or high for 4 hours. If you’re worried about the chicken breasts drying out while cooking, you can add 1/4-1/2 cup of water to the slow cooker.
When chicken is cooked through, remove it from the slow cooker and shed it using two forks. If it’s not tender enough, cook it longer.
Place the chicken back in the slow cooker and pour the BBQ sauce over the shredded chicken. Stir to mix so all of the chicken is well coated with sauce.
Replace the lid and allow to heat for 10 more minutes before serving.