Place chicken breasts in the bottom of the crockpot.
In a mixing bowl, whisk pineapple juice, soy sauce, brown sugar, garlic, ketchup, and ginger.
Pour the sauce evenly over the chicken.
Add pineapple chunks on top.
Cover and cook on low for 4 hours or until chicken is tender.
Remove chicken and shred or slice if desired.
(Optional) Mix cornstarch and water, stir into the sauce, and cook 10 minutes to thicken.
Return chicken to the crockpot and coat with sauce.
Garnish with chopped green onions before serving.