Rub jerk seasoning generously over chicken. Place bell pepper and onion in bottom of 3 1/2- to 4-quart slow cooker. Place chicken over vegetables. Mix broth and ketchup in small bowl; pour over chicken.
Cover and cook on low heat setting 6 to 8 hours.
Remove chicken from cooker; place on cutting board. Shred chicken, using 2 forks. Return chicken to cooker and mix well. Using slotted spoon to remove chicken mixture from cooker, fill buns with chicken mixture.