Cut redfish filets diagonally into 2½-inch strips.
Heat oil over medium high heat in a 1 gallon heavy bottom sauce pan. Using a wire whisk, add flour and cook, stirring constantly, until dark brown roux is achieved. Add onions, celery, bell pepper, garlic, and mushrooms and sauté until vegetables are wilted (3 to 5 minutes).
Add tomato sauce and blend well. Slowly add fish stock, stirring constantly to mix well. Add thyme, basil, bay leaves, and lemon and bring to a low boil then reduce heat and simmer 30 minutes. Add green onions and parsley and season to taste with salt, pepper, and pepper sauce.
Cook 10 more minutes then add the fish; cook, stirring gently occasionally, until fish is just opaque through, 5 to 10 minutes. Serve hot with plenty of French bread.