Heat oil or butter in a large pot over medium heat
Whisk in flour to make a roux
Cook the roux, stirring constantly, until it turns dark brown
Add chopped onion, celery, and bell pepper
Cook until the vegetables soften
Add garlic and cook briefly
Stir in broth or stock
Add sliced sausage, chicken, or seafood
Add okra or filé powder if desired
Add bay leaves, thyme, salt, black pepper, and cayenne
Simmer until the meat is cooked and the flavors blend
Add cooked rice to serving bowls
Ladle the gumbo over the rice
Garnish with green onions or parsley if desired