1. Thaw fish, if frozen. Rinse fish; pat dry with paper towels. Cut into 4 serving-size pieces, if necessary. Arrange fish in a 2-quart rectangular baking dish, turning under thin edges. Sprinkle with salt.

2. In a small saucepan melt butter; add mushrooms, green onions, and dried tarragon, if using. Cook over medium heat until mushrooms and green onions are tender. Spoon mushroom mixture over fish; sprinkle with fresh tarragon, if using. Bake, covered, in a 450 F oven for 12 to 18 minutes or until fish flakes easily when tested with a fork.