Combine oil and flour in a large stock pot; cook over medium heat 30 minutes or until roux is the color of a copper penny, stirring frequently.
Stir in green pepper, onion, celery, and garlic; cook, stirring frequently, 15 minutes or until vegetables are tender. Add tomatoes; cook, uncovered, over low heat 1 hour or until oil begins to separate around edge of stock pot; stir occasionally.
Stir in next 8 ingredients; cook, uncovered, 30 minutes, stirring occasionally. Add fish, and cook 20 minutes or until fish flakes easily when tested with a fork.
Serve over hot cooked rice in individual serving bowls. Garnish with chopped green onion and lemon wedges.