Pat the chicken breasts dry, then rub them with the jerk paste and add the chopped onion.
Cover and marinate in the refrigerator for at least 1 hour.
In a bowl, mix together the BBQ sauce, Worcestershire sauce, brown sugar, and jerk paste.
Add the chicken to the slow cooker and pour the sauce over it, turning the chicken to coat.
Cover and cook on high for 3½ hours, or until the chicken is tender and has reached an internal temperature of 165°F.
Remove the chicken from the slow cooker and shred it using two forks.
Return the shredded chicken to the slow cooker and stir it into the sauce. Let it sit in the sauce for 10 minutes so the chicken can soak up more of the flavor.
Fill the French rolls with the pulled jerk chicken and top with pineapple chutney.