1. Heat the oil in a large pot over medium heat. Gradually stir in the flour, and cook, stirring constantly, until the roux reaches a deep brown color.
2. Stir in the onion, bell pepper, celery, and garlic; cook until the vegetables are tender, about 5 minutes.
3. Mix in the sausage and chicken, and cook for about 5 minutes.
4. Gradually stir in the chicken stock. Bring to a boil, then reduce heat to low, and simmer for 45 minutes.
5. Stir in the okra, and simmer for an additional 30 minutes.
6. Season with salt, black pepper, cayenne pepper, Creole seasoning, and bay leaves. Simmer for 10 more minutes.
7. Serve gumbo over cooked white rice, and garnish with green onions and parsley.