In a bowl, combine the onions, bell peppers, okra and celery; set aside.
Combine all but 1/2 cup of the flour, the salt, garlic powder, and red pepper in a plastic bag, add the chicken pieces and shake until chicken is well coated. In large heavy skillet heat 1 1/2-inches of oil until very hot (375 degrees F.) Fry the chicken until the crust is brown on both sides and meat is cooked, about 5 to 8 minutes per side; drain on paper towels.
Remove the pan from the heat and pour the hot oil into a cup, leaving as many brown particles in the pan as possible. Scrape the bottom of the pan with a wooden spoon to loosen any stuck particles, then return 1/2 cup of the hot oil to the pan. Place the pan over high heat. Using a long handled whisk, gradually stir in remaining flour. Cook, whisking constantly, until a roux is formed and is a dark red-brown. Remove from heat and add the reserved vegetable mixture, stirring constantly until the roux stops getting darker. Return to a low heat and cook until the vegetables are soft.
In a separate large pot, bring the chicken stock to a boil. Add the roux by spoonfuls to the boiling stock, stirring between each addition. Reduce to a simmer and add the andouille and remaining ingredients, except file powder. Simmer for 45 minutes. While gumbo is simmering, bone the cooked chicken and cut meat into 1/2-inch dice. Add to the gumbo. Add file powder 5 minutes before serving and continue to simmer for 5 minutes.
Serve gumbo on a mound of cooked rice.
Recipes reprinted with permission DM Cuisine, Ltd. Created by Chef Daniel Mattrocce