Step 1Rinse fish and pat dry. Lightly season with salt.
Step 2Heat large skillet over medium-high heat. Add oil. When hot, add onion and cook, stirring frequently, until softened but not browned, 5 minutes.
Step 3Add tomatoes and cook, stirring occasionally, 5 minutes.
Step 4Place fish on top of tomatoes, setting thicker portions around edges of skillet. Pour wine over fish and sprinkle with parsley. Cover and bring to simmer. Reduce heat and simmer until fish is cooked through, 10 minutes. You may need to shift fish in pan halfway through cooking if filets on edges are cooking more quickly than those in middle. Remove fish to serving platter and cover with foil.
Step 5Bring wine and tomato mixture to boil and cook about 3 minutes to reduce slightly. Pour over fish.