1.
In a medium sauté pan, lightly brown onion and garlic in oil for several minutes. Add tomatoes and cook on medium-high for 5 to 10 minutes to reduce liquid. Add vinegar and oregano.
2.
Single layer fish in oiled baking dish. Sprinkle with olives, capers, and lemon juice. Pour sauce over fish and bake at 375 degrees for about 20 minutes (until fish flakes with a fork).