Preheat the oven to 450°F. Rinse the halibut and pat dry with paper towels; place into a greased 13x9-inch baking dish. Sprinkle the halibut with salt.
In a small bowl, combine the Swiss cheese, sour cream, yogurt and 2 tablespoons green onion. Spread the sour cream mixture evenly over the halibut; sprinkle with Parmesan cheese.
Bake for 12 to 15 minutes, or until the halibut flakes with a fork; sprinkle with the remaining green onion.