1. Heat oil in a large pan over medium heat. Add onion, and cook for 8 minutes. Reduce heat to low. Add cumin, cook for 3 more minutes.
2. Place fish fillets on the onion mixture. Cook for 3 minutes; turn to coat other side and cook for additional 3 minutes.
3. Prepare the sauce. In a small bowl, mix cayenne pepper, garlic, parsley, tomato, tomato sauce, and salt. Pour mixture over fish. Add water to cover fish (approximately 1/2 cup), if necessary. Cook, uncovered, on low for an additional 15 minutes.