Stir in the onion, bell pepper and celery and increase the heat to medium and cook until the vegetables are softened, 8 to 10 minutes. Whisk in the stock and water and bring to a simmer. Add the chicken, sausage along with any accumulated juices and simmer until the chicken is cooked through, about 30 minutes. Stir in the okra and cook until tender, 4 to 8 minutes. Season the gumbo with salt and pepper to taste, then stir in the rice and serve sprinkled with the scal-lions.