Preparation Preheat oven to 450°F with rack in middle. Pat fish dry in a small shallow baking pan and drizzle with 1/2 tablespoon oil, then sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper. Toss mushrooms with remaining 2 tablespoons oil and 1/4 teaspoon each of salt and pepper, then spread in another small shallow baking pan. Roast fish and mushrooms, stirring mushrooms once or twice, until fish is just cooked through and mushrooms are crisp, about 10 minutes. Meanwhile, prepare soup according to package instructions. Divide soup, mushrooms, and fish among 4 bowls and top with scallion.
Preparation Preheat oven to 450°F with rack in middle. Pat fish dry in a small shallow baking pan and drizzle with 1/2 tablespoon oil, then sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper. Toss mushrooms with remaining 2 tablespoons oil and 1/4 teaspoon each of salt and pepper, then spread in another small shallow baking pan. Roast fish and mushrooms, stirring mushrooms once or twice, until fish is just cooked through and mushrooms are crisp, about 10 minutes. Meanwhile, prepare soup according to package instructions. Divide soup, mushrooms, and fish among 4 bowls and top with scallion.