Preheat oven to 250F. Make light roux with flour and oil. Add chopped onions, tomato sauce and Rotel tomatoes to roux. Cook in covered pot for 30 minutes on low heat, stirring occasionally to prevent sticking. Add water, a little at a time, and mix thoroughly. Let cook, on low heat, for 1 hour. Check occasionally to prevent boiling over and sticking.
While gravy is cooking, cut fish 2 inch thick. Make incision with thin bladed knife and insert mixture of chopped cayenne, bell peppers, garlic, salt and red pepper. After gravy has cooked 1 hour, add fish chunks and cook for 30 minutes, stirring carefully to keep from breaking fish. Add onion tops and parsley to taste.
Cajun Country -- New Iberia, Louisiana