01 - Place the chicken thighs or breasts in an even layer at the bottom of the slow cooker insert.
02 - In a medium bowl, whisk together the pineapple juice, soy sauce, brown sugar, ketchup, rice vinegar, minced garlic, and grated ginger until the sugar dissolves completely.
03 - Pour the sauce mixture evenly over the chicken. Arrange the sliced onion, bell pepper pieces, and pineapple chunks on top of the chicken and sauce.
04 - Cover the slow cooker with its lid. Cook on LOW setting for 4 to 5 hours, or until the chicken reaches an internal temperature of 165°F and is tender enough to shred easily.
05 - Remove the cooked chicken and vegetables from the slow cooker using a slotted spoon. Transfer to a serving platter and cover loosely with aluminum foil to keep warm.
06 - In a small bowl, whisk together the cornstarch and water until smooth and no lumps remain.
07 - Pour the cooking liquid from the slow cooker into a medium saucepan. Bring to a simmer over medium heat. Gradually whisk in the cornstarch slurry while stirring constantly. Continue cooking for 2 to 3 minutes until the sauce thickens enough to coat the back of a spoon.
08 - Pour the thickened sauce over the chicken and vegetables on the serving platter. Sprinkle with sliced green onions and sesame seeds if desired. Serve immediately while hot, accompanied by steamed white or coconut rice.