Combine vinegar, oil, basil, and pepper in 8 x 8-inch glass dish. Add salmon and turn to coat both sides. Marinate 15 to 30 minutes, turning once. Drain marinade into 4-cup glass measure. Add mushrooms and green onions and stir to coat well. Place salmon in glass dish. Cover with waxed paper. Microwave at HIGH 4 minutes, turning dish once, and let stand, covered, minutes. Fish is done when it just begins to flake easily when tested with a fork. Microwave mushroom mixture, uncovered, at HIGH 3 minutes, stirring once. Transfer salmon to hot plates and spoon mushrooms over top.
