In a large pot or Dutch oven, heat the vegetable oil over medium heat. Gradually stir in flour to make a roux. Stir constantly until roux turns a dark brown color, about 20-30 minutes.
Add onion, bell pepper, celery, and garlic to roux. Cook, stirring frequently, until vegetables are tender, about 5 minutes.
Stir in sausage and chicken. Season with salt, black pepper, cayenne pepper, thyme, oregano, and bay leaves. Cook for another 5 minutes, so chicken browns slightly.
Slowly add chicken broth and diced tomatoes to pot, stirring. Bring mixture to a boil, then reduce heat and simmer for about 45 minutes.
Add shrimp to pot and cook until pink and opaque, about 5 minutes.
Remove and discard bay leaves. Just before serving, stir in cooked rice, parsley, and scallions.
Variations & Tips
For a seafood-only gumbo, you can omit the chicken and sausage and add more shrimp, crabmeat, or even crawfish if you can find it. If you prefer a spicier gumbo, feel free to use more cayenne pepper or add a few dashes of hot sauce. For a vegetarian variation, omit the meat and use vegetable broth. For extra texture, you can add okra or mushrooms. To save time, you can make the roux ahead of time and store it in the refrigerator for up to a week.
