Begin by cutting the chicken breasts into 1-inch cubes. Place the cubed chicken into the slow cooker. Pour in the crushed pineapple and barbecue sauce, then stir everything together until well-mixed.
Set the slow cooker to low and cook for 3.5 to 4 hours, or if you're in a hurry, cook on high for 2 to 2.5 hours. If you're using frozen chicken cubes, extend the cooking time by an additional 30 to 45 minutes.
The chicken is ready when it reaches an internal temperature of 165°F (74°C), is fork-tender, and the sauce has thickened and is bubbling gently. Carefully remove the lid, spoon the chicken mixture onto plates, and if desired, garnish with fresh lime and cilantro.