For the Roux:

• 1/2 cup vegetable oil
• 1/2 cup all-purpose flour

For the Gumbo:

• 1 medium onion, chopped
• 1 green bell pepper, chopped
• 2 celery stalks, chopped
• 4 cloves garlic, minced
• 1 (14.5-ounce) can diced tomatoes (optional)
• 6 cups seafood or chicken stock
• 2 bay leaves
• 1 teaspoon dried thyme
• 1/2 teaspoon cayenne pepper (adjust to taste)
• 1 teaspoon paprika
• 1/2 teaspoon black pepper
• 1 teaspoon salt (or to taste)
• 1 tablespoon Worcestershire sauce
• 1 pound andouille sausage, sliced
• 1 pound raw shrimp, peeled and deveined
• 1/2 pound lump crabmeat, picked over for shells
• 1/2 pound shucked oysters (optional)
• 2 tablespoons chopped parsley
• 3 green onions, sliced
• cooked white rice for serving
• file powder (optional, for serving)