Add the chicken pieces to the slow cooker.
Place the sliced red and green bell peppers and pineapple chunks on top of the chicken.
In a bowl, stir together the pineapple juice, ketchup, apple cider vinegar, brown sugar, and soy sauce until the sugar dissolves.
Pour the sauce mixture over the chicken and vegetables in the slow cooker.
Cover and cook on low for 5 to 6 hours until the chicken reaches an internal temperature of 165°F.
In a small cup, mix the cornstarch with 2 tablespoons of cold water, then stir the slurry into the slow cooker.
Cook on high for 15 more minutes to thicken the sauce.
Sprinkle the sliced green onions over the dish before serving.