Combine the soy sauce, tomato paste, Worcestershire sauce, garlic powder, brown sugar, and black pepper directly in the base of your slow cooker, stirring until well integrated.
Introduce the cubed chicken, chopped red bell pepper, and entire contents of the pineapple can, including its juice, to the slow cooker.
Carefully mix all components until the chicken and vegetables are thoroughly coated with the seasoned mixture.
Secure the lid and set the slow cooker on low; allow the ingredients to simmer gently for 4 to 6 hours, or alternatively, cook on high for 2 to 3 hours.
Roughly 30 minutes before completion, evaluate the seasoning of the sauce and adjust as needed—additional soy sauce or brown sugar may be incorporated according to preference.
Optionally, sprinkle with scallions just before serving and present over a bed of steamed rice if desired.