01 - Place the chicken thighs or breasts in the bottom of the slow cooker.
02 - In a medium bowl, whisk together the pineapple juice, soy sauce, brown sugar, ketchup, rice vinegar, garlic, and ginger until well combined.
03 - Pour the sauce mixture over the chicken. Arrange the onion, bell peppers, and pineapple chunks on top.
04 - Cover and cook on LOW for 4-5 hours, or until the chicken is tender and reaches an internal temperature of 165°F.
05 - Transfer the chicken and vegetables to a serving platter and cover loosely with foil to keep warm.
06 - In a small bowl, mix the cornstarch and water until smooth to form a slurry.
07 - Pour the cooking liquid from the slow cooker into a saucepan. Bring to a simmer over medium heat, then whisk in the cornstarch slurry. Cook for 2-3 minutes, stirring constantly, until the sauce thickens.
08 - Pour the thickened sauce over the chicken and vegetables. Garnish with green onions and sesame seeds if desired. Serve hot with steamed rice.