Heat oil In a 2-gallon stockpot over medium-high heat. Whisk in flour, stirring constantly, until golden brown roux is achieved, up to 10 to 20 minutes.
Stir in onions, celery, bell peppers, and garlic. Sauté until vegetables are wilted. 3 to 5 minutes. Add sausage into vegetable mixture, and sauté for approximately 15 minutes. Stir in chicken.
Add chicken stock, a little at a time, stirring constantly. Bring to a rolling boil, reduce to simmer and cook approximately 1 hour. Stir in green onions and bay leaves. Season with Cajun seasoning, file, and hot sauce. Cook an additional 30 minutes, if necessary, until the chicken is tender and falling apart. Stir in parsley and adjust seasonings. Serve over steamed white rice; garnish with green onions.