Rinse the fish thoroughly inside and out, making sure the cavity is clean. Transfer to a heatproof, steamer-safe dish and pat dry with paper towels.
1 whole white fish
Season both sides and the cavity of the fish evenly with salt. Scatter the chopped green onions and ginger over the top.
¼ teaspoon salt, 2 green onions, 2 inch ginger
In a small bowl, mix the soy sauce, sugar, and sesame oil. Set aside.
2 tablespoon soy sauce, 1 teaspoon granulated sugar, 1 teaspoon sesame oil
Add water to a wok or pot fitted with a steamer and bring to a low boil. Place the fish into the steamer, cover, and steam for 10-13 minutes, depending on the size of the fish, until the flesh turns opaque and flakes easily.
Carefully remove the fish from the steamer and drain off any excess liquid from the dish.
Spoon the prepared sauce evenly over the fish.
Garnish with additional sliced ginger and scallions if desired, and serve immediately.