Gently stir the ingredients in the slow cooker, ensuring the chicken and bell peppers are evenly coated in the marinade. Set your slow cooker to low and cover it with the lid. Cook on low for 4-6 hours or high for 2-3 hours.
About 30 minutes before serving, taste the sauce and adjust the seasoning if necessary. You can add more soy sauce or brown sugar if desired. Optionally, garnish with sliced scallions ad serve over rice.