Heat the oil in a large skillet over medium-high heat. Cook and stir the bell pepper and onion in the oil until slightly tender, 5 to 7 minutes. Remove pepper and onion from the skillet and set aside. Add the chicken to the skillet; season with jerk seasoning; cook and stir chicken until no longer pink inside. Pour the plum sauce in with the chicken; add the bell peppers and onions; toss to combine. Cook until the peppers and onions are heated completely, 3 to 5 minutes. Sprinkle with soy sauce and chopped peanuts to serve.