Prep the Crockpot: Spray or lightly oil the inside of your slow cooker.
Add Chicken + Veggies: Arrange chicken pieces (3 pounds), diced bell pepper, and onion in the crockpot.
Make the Sauce: In a bowl, whisk together pineapple juice (1 cup), soy sauce (1/2 cup), brown sugar (1/2 cup), ketchup (1/2 cup), garlic (1 teaspoon), ginger (1/2 teaspoon), vinegar (2 tablespoons) (if using), and black pepper (1/8 teaspoon). Pour over the chicken. Add the drained pineapple chunks (1 can).
Cook: Cover and cook on LOW 4–6 hours or HIGH 2½–4 hours until the chicken is tender and cooked through. Timing may vary slightly with different slow cooker models.
Thicken: About 30 minutes before serving, whisk cornstarch (3 tablespoons) and cold water (3 tablespoons) until smooth and stir into the crockpot. Add butter (2 tablespoons). Replace the lid and let the sauce thicken.
Serve: Spoon chicken and sauce over warm rice. Garnish with green onions and sesame seeds if desired.
Notes
Use thighs if you want ultra-tender chicken. Chicken thighs stay juicy even after hours in the slow cooker, which makes them perfect for saucy crockpot recipes. Breasts work too, but they’ll be a little firmer in texture.
Finish with butter for a richer, smoother sauce. After thickening the sauce, stirring in a tablespoon or two of butter makes a big difference. It softens the acidity, adds shine, and gives the sauce that cozy, restaurant-style mouthfeel — especially when spooned over hot rice.
Want pineapple chunks in the final dish? Add them at the end. If you like visible pineapple pieces, stir in drained pineapple chunks during the last 20–30 minutes of cooking. Adding them earlier can make them overly soft and muted in flavor.
Don’t overcook once the sauce is thick. Once the cornstarch slurry goes in and the sauce thickens, it’s best to serve soon. Long extra cooking can make the sauce tighten up more than you want.