In a large heavy bottom saucepan, pour enough oil to fill the pan about a third of the way. Heat over medium heat until a deep-fryer thermometer inserted in the oil reaches 350 degrees F. (If you do not have a thermometer a cube of bread will brown in about 3 minutes.)
In a bowl whisk together the egg whites, cornstarch, salt, and pepper, to taste. Dip the shrimp into the egg mixture, and then press the shrimp into the coconut flakes, coating well on both sides.
Fry the shrimp in batches until coconut is golden, about 2 to 3 minutes. Drain on paper towel. Serve immediately.
Dress shrimp with lime dressing and garnish with watercress leaves.
Combine ingredients in a small bowl, and chill until ready to serve.