Heat oil in large nonstick skillet. Add onion, and sauté over moderate heat 5 minutes or until soft.
Add all remaining ingredients except fish.
Stir well and simmer 30 minutes, uncovered.
Arrange fish in 9x11 baking dish; cover with sauce.
Bake, uncovered, at 375º F about 15 minutes or until fish flakes easily.
Serving Size 4 servings