Make the roux: In a heavy-bottomed pot, heat oil over medium heat. Whisk in flour to form a roux. Stir constantly for about 10–15 minutes or until the roux is a deep peanut butter color.
Sauté vegetables: Add onions, bell pepper, and celery. Sauté for 5 minutes until softened. Add garlic and cook 1 more minute.
Build the base: Stir in tomato paste and cook for 2 minutes. Add diced tomatoes, stock, bay leaves, thyme, Worcestershire sauce, K’s Kreole Seasoning, pepper, and sugar if using. Bring to a simmer.
Simmer and thicken: Simmer uncovered for 20–30 minutes until flavors meld and sauce thickens slightly.
Add catfish: Gently place catfish into the stew. Simmer another 10–12 minutes or until fish is cooked through and tender (do not stir too vigorously to avoid breaking the fish).
Finish and serve: Stir in lemon juice, parsley, and green onions. Adjust seasoning to taste.
Serve hot over steamed rice with hot sauce and a slice of French bread.