Melt the butter in a large dutch oven or stock pot over medium/high heat.
Whisk in the flour and continue whisking until the mixture starts to turn golden brown and smell nutty, approximately 3-4 minutes. (Do not stop whisking or the roux will burn.)
Stir in the onion, bell pepper and celery. Continue cooking for 2-3 minutes, stirring constantly, until the vegetables begin to soften.
Add the sausage to the pot and stir to combine. Cook for 1 minute longer.
Stir in the garlic, mustard, cayenne, paprika, garlic powder and creole seasoning. Cook for 1 minute longer, stirring constantly and scraping up any brown bit on the bottom of the pan.
Slowly add the chicken stock to the pot stirring to combine. Add the chicken and bring the soup to a boil.
Turn the heat to low. Add the bay leaf, okra, salt and pepper to the soup and stir to combine. Simmer for 10 minutes or until the soup begins to thicken.
Serve the chicken gumbo over rice, if desired. Sprinkle with chopped green onions and parsley for an extra pop of color.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)