- In a large bowl, combine pineapple juice, soy sauce, brown sugar, garlic, ginger, black pepper, and red pepper flakes. Whisk until well mixed. 
- Place the chicken thighs in the crockpot and pour the sauce mixture over them, ensuring the chicken is well coated. 
- Add the diced bell peppers and onions on top of the chicken. 
- Cover and cook on low for 6-8 hours or on high for 3-4 hours, until the chicken is tender and fully cooked. 
- Once cooked, shred the chicken in the crockpot using two forks and stir to combine with the sauce and vegetables. 
- Serve the sweet Hawaiian chicken over cooked rice and garnish with chopped green onions.