Prepare the chicken: Lightly grease the slow cooker and place the chicken in the bottom.
Mix the sauce: In a bowl, whisk together pineapple juice (from the can), soy sauce, brown sugar, ketchup, garlic, and ginger.
Cook: Pour the sauce over the chicken. Cover and cook on Low for 5–6 hours or High for 3–4 hours, until the chicken is tender.
Add pineapple: About 30 minutes before serving, stir in the pineapple chunks.
Thicken the sauce (optional): Mix cornstarch and water in a small bowl, then stir into the crockpot. Cook uncovered for 20–30 minutes until the sauce thickens.
Serve: Garnish with green onions and sesame seeds. Serve hot over rice or with roasted vegetables.