Add the chicken breasts to the slow cooker. Scatter the sliced onion and minced garlic over the top.
Sprinkle the smoked paprika, salt, and black pepper evenly across the chicken.
Pour the barbecue sauce over everything and turn the chicken pieces so they are coated on all sides.
Cover and cook on low for 6 to 7 hours, until the chicken shreds easily with a fork.
Use two forks to pull the chicken apart directly in the slow cooker, then stir it through the sauce and onions.
Spoon the pulled chicken onto the buns and top each sandwich with several slices of pickle.