Heat oil in large non-stick skillet over medium heat.
Add onion and cook, stirring frequently until onion is golden
brown, about five minutes; add garlic and cook for 1 minute longer. Add tomatoes cook, stirring, for 2 minutes; stir in vinegar.
Push tomato mixture to one side of skillet. Add water. When liquid
starts to simmer, add fish and cover the skillet. Cook til fish flakes
easily, about 8 to 10 minutes.
Remove fish and arrange on serving platter. Add pepper to taste to the
tomato mixture and stir. Spoon the tomato mixture over the fish and serve