Add the butter to a large, heavy-based pot over MEDIUM heat. Once the butter has melted, sprinkle in the flour. Stir slowly until it forms a smooth, caramel-colored roux.
Add the diced onion, celery, peppers, and garlic. Saute for 5 minutes.
Add the duck, crushed tomato, chicken stock, bay leaves, Creole seasoning, and salt and pepper to the pot. Stir. Cover the pot and bring the mix to a boil. Turn down the heat and let simmer for 45 minutes, stirring occasionally.
If the gumbo hasn’t thickened, remove the lid and continue to let simmer. Add the shrimp and cook for 5 minutes, until the shrimp has turned an opaque white.
Remove the bay leaves. Sprinkle the green onions over and serve. Enjoy!