Start by trimming the boneless, skinless chicken breasts to remove any excess fat. Place the chicken in the slow cooker, ensuring it's evenly distributed at the bottom for even cooking.

In a medium bowl, combine the pineapple juice, diced pineapple, soy sauce, brown sugar, minced garlic, ground ginger, and black pepper. Whisk together until the brown sugar dissolves.

Pour the prepared pineapple sauce over the chicken in the slow cooker, ensuring that each piece is well-coated. Mix gently with a wooden spoon.

Cover the slow cooker with its lid and set it to cook on low for 6-8 hours or on high for 3-4 hours. Ensure the chicken reaches an internal temperature of 165°F.

Once cooked, shred the chicken directly in the crockpot using two forks, mixing it into the sauce.

To serve, ladle the chicken and sauce onto a plate or bowl, garnishing with sliced green onions and sesame seeds. Serve over rice or quinoa.