Preheat the oven to 425 degrees F. Line a shallow baking dish with parchment paper. Set in the salmon and drizzle it with the butter and lemon juice. Season with salt and pepper. Bake for 12 to 15 minutes, or until just cooked through. While the fish cooks, place the sherry and ginger in a small pot, set over medium heat. Bring to a simmer and reduce by half. Add the whipping cream and simmer until a lightly thickened sauce forms; season with salt and pepper.
Pour a pool of the sauce on each of 4 plates. Set a piece of salmon on each plate. Sprinkle with the green onions and serve.