Place the chicken pieces in the slow cooker. Add the sliced red and green bell peppers along with the pineapple chunks.
In a small bowl, whisk together the pineapple juice, rice vinegar, ketchup, brown sugar, soy sauce, and minced garlic until smooth.
Pour the sauce mixture over the chicken and vegetables in the slow cooker. Stir gently to coat everything evenly.
Cover and cook on low for 4 to 5 hours or until the chicken reaches an internal temperature of 165 degrees.
In a small cup, mix the cornstarch with the water to form a slurry. Stir the slurry into the slow cooker during the last 30 minutes of cooking to thicken the sauce.
Serve the chicken and sauce over cooked rice and top with sliced green onions.