Foil-pack dinners are a convenient way to quickly create a flavorful dish with practically no cleanup. In this foil-pack, the salmon and vegetables are simply cooked, then finished with a bright, assertive ginger-scallion butter.
Lay out four 18-inch-long sheets of heavy-duty foil. Mound 1/2 cup mushrooms and 1 cup spinach in the center of each; season with salt and pepper. Top each with a salmon fillet, season with salt and pepper and drizzle with olive oil. Drizzle each with 1 tablespoon wine (or water). Bring the short ends of the foil together and fold twice to seal; fold in the sides to form a packet, leaving room inside for steam.
Preheat a grill to medium high. Grill the foil packets until the fish is just cooked through, 10 to 12 minutes. (Alternatively, you can bake the foil packets in a 450˚ F oven until the fish is just cooked through, 12 to 15 minutes.) Let the packets sit 5 minutes.
Meanwhile, combine the butter, scallions, ginger, sesame oil and 1/4 teaspoon salt in a mini food processor. Pulse until smooth. Carefully open the foil packets. Top with the flavored butter.