Begin by preparing your ingredients. Slice the bell pepper and onion, and if using fresh pineapple, cut it into chunks.
In the slow cooker, place the chicken breasts at the bottom.
In a medium bowl, combine the soy sauce, brown sugar, minced garlic, minced ginger, sesame oil, and black pepper. Mix well until the sugar dissolves.
Pour the mixture over the chicken in the slow cooker.
Add the sliced bell pepper, onion, and pineapple chunks on top of the chicken.
Cover the slow cooker and cook on low for 4 hours, or until the chicken is tender and cooked through.
Once cooked, shred the chicken using two forks or serve it whole.
Serve the Hawaiian chicken over cooked rice and garnish with chopped green onions.