Place the chicken pieces, sliced bell pepper, chopped onion, minced garlic, and grated ginger into the slow cooker.
In a bowl, whisk together the ketchup, rice vinegar, brown sugar, soy sauce, and 1/2 cup of the reserved pineapple juice until smooth.
Pour the sauce over the chicken and vegetables in the slow cooker. Stir gently to coat everything.
Cover and cook on low for 6 hours or on high for 3 hours until the chicken is tender.
About 30 minutes before serving, combine the rice, chicken broth, and remaining pineapple chunks with their juice in a medium saucepan.
Bring the rice mixture to a boil, then reduce to low, cover, and simmer for 18 minutes until the liquid is absorbed and rice is fluffy.
Fluff the rice with a fork and divide it among four bowls. Spoon the sweet and sour chicken and vegetables over the rice.
Sprinkle sliced green onions on top before serving.