With the rack in the middle position, preheat the oven to 500°F (260°C). Line a baking sheet with aluminum foil.
In a bowl, beat the egg whites with an electric mixer until stiff peaks form. With a wooden spoon, stir in the salt. Set aside.
Stuff the cavity of the fish with the green onion, garlic, bay leaves and thyme.
On the baking sheet, spread a third of the salt mixture to the approximate dimensions of the fish. Place the fish on the salt and completely cover with the remaining salt mixture.
Bake for 25 minutes or until the salt crust is golden brown.
Meanwhile, in a bowl, combine all of the ingredients.
Break the crust around the fish. With a fork, gently detach the skin from the fish and remove the fillet. Remove the central bone, pulling it away from the tail toward the head. Remove the bottom fillet.