Combine soy sauce, garlic, black pepper, and brown sugar in a small bowl. Stir until combined.

Place chicken in the bottom of the slow cooker, cover with pineapples, and top with sauce.

Cook on low for 6-8 hours.

During the last hour of cooking, add in bell pepper slices.

To thicken the sauce, also remove the lid from the slow cooker in the last hour of cooking. If you prefer a thicker sauce, transfer the sauce to a pan and boil with flour or cornstarch until reduced to desired thickness.