Place chicken in a slow cooker, set aside. In a mixing bowl, whisk together soy sauce, apple cider vinegar, light-brown sugar, honey, orange marmalade, ginger, garlic and pepper. Pour mixture over chicken in slow cooker, cover with lid and cook on low heat 4 - 5 hours.
Remove chicken from slow cooker and shred. Strain sauce from slow cooker through a fine mesh strainer into a medium saucepan. In a small mixing bowl whisk together 1 1/2 Tbsp cold water and cornstarch. Pour cornstarch mixture into liquid in saucepan and heat mixture over medium high heat, stirring constantly, until mixture begins to gently boil.
Allow mixture to gently boil about 20 seconds until thickened. Return chicken to slow cooker and pour teriyaki sauce from saucepan over chicken. Toss mixture gently to evenly coat. Serve warm over cooked rice garnished with optional sesame seeds and serve with diced fresh pineapple if desired.