Pre-heat oven to 400 degrees.
Stuff fish with grapefruit slices, lime slices, and mint leaves (see recipe notes for alternative stuffing)
In a large bowl, mix together kosher salt and egg whites until mixture resembles wet sand.
Spread about 1 cup of the mixture on the bottom of a large baking sheet to create a "bed" for the fish. Lay the fish on the bed. Use the rest of the salt mixture to completely coat the fish, gently pressing down.
Bake fish for about 30 minutes (or until fish has an internal temperature of about 135 degrees). Remove from oven and let cool slightly, about 5 minutes.
Use a mallet to gently crack the salt coating away from the fish.
Serve fish as is or remove the skin and fillet before serving.