Preheat the oven to 400 degrees F. Line a baking sheet with parchment.
Combine the egg whites and salt in a large bowl; mix with your hands until it resembles wet sand. Spread about 1 cup of the salt mixture on the baking sheet. Lay the fish on salt; stuff the cavity with the cilantro, lime and some pepper. Grind pepper over the outside of the fish, as well. Mold the remaining salt mixture over the fish and seal tightly.
Transfer to the oven and cook until an internal temperature of 125 degrees F is reached, 30 to 40 minutes. Remove from the oven. Crack the salt crust off using the back of a knife. Transfer the fish to a cutting board, remove any remaining salt, and then fillet. Transfer the fillets to a serving platter. Serve immediately.