1. Make the dressing: Place all ingredients in a blender and process until smooth. Transfer to a bowl and reserve.
2. Make the oysters: In a bowl, mix oysters and egg whites together. In a separate bowl, whisk together the masa, cayenne, and 1 tablespoon of the salt. In a large cast-iron skillet fitted with a deep-fry thermometer, bring TK inches of oil to 300-325 degrees over medium-high heat. Dredge a few oysters in the masa and fry until golden brown, about 1 minute. Drain on paper towel-lined sheet tray. Repeat with remaining oysters. Sprinkle oysters with spring onions and remaining salt and serve with the dressing on the side.