1. Prepare the chicken by trimming any excess fat from boneless, skinless chicken thighs or breasts. Season the chicken lightly with salt and pepper.
2. In a medium bowl, mix brown sugar, ketchup, soy sauce, crushed red pepper flakes, minced garlic, and freshly grated ginger to prepare the sauce. Stir until fully combined.
3. Place the seasoned chicken pieces into the crock pot. Add red bell pepper and onion slices over the chicken. Pour the prepared sauce evenly over the top to coat the chicken.
4. Set the crock pot to LOW heat and cook for 4 to 6 hours, or set it to HIGH heat and cook for 3 to 4 hours, allowing the flavors to combine and the chicken to become tender.
5. To thicken the sauce, mix 1 tablespoon of cornstarch with an equal amount of water to form a slurry. Add it to the crock pot, then set the heat to HIGH for 15 minutes, stirring occasionally, until the sauce reaches the desired consistency.
6. Once done, garnish the dish with green onions, sesame seeds, or slivered almonds, based on your preference.
7. Serve the chicken hot over steamed rice, in a sandwich, with Hawaiian rolls, or with your choice of side dish. Enjoy your Crock Pot Sticky Hawaiian Chicken!