Sprinkle the fish with salt and pepper. Heat olive oil in a large nonstick skillet over medium-high heat. Add fish and onion; cook for 3 minutes. Turn fish over. Stir in wine, vinegar, and capers; cook 3 minutes. Remove fish from pan. Cook wine mixture an additional 3 minutes or until reduced to 1/2 cup. Serve sauce with fish; sprinkle with parsley.