Remove green tops from onions; slice onion tops into 1-inch pieces to measure 1/4 cup; set aside. Reserve remaining onion tops for another use. Cut white portions of onions into 2-inch pieces.
Combine cilantro, ginger, and 1 teaspoon oil in a 9-inch pie plate. Fold each fillet in half crosswise. Arrange fish spokelike with thinnest portions pointing toward center of dish. Arrange white onion portions between each fillet. Combine 1/4 cup green onion tops, 1 teaspoon oil, vinegar, soy sauce, and salt; pour over fish. Cover with heavy-duty plastic wrap. Microwave at HIGH 4 minutes or until fish flakes easily when tested with a fork. Garnish each fillet with a lemon slice.
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