Preheat the oven to 400 degrees F.
In a blender, combine the egg, mustard, hot sauce, lemon juice, Worcestershire, salt, black pepper, and red pepper flakes. Process until smooth, about 30 seconds. With the motor running, pour in the oil in a slow, steady stream. The mixture will thicken. Refrigerate until ready to use.
Put the scallop shells on a baking sheet. Season both sides of the scallops with the salt and black pepper. Place 2 scallops in each shell and spoon about 2 tablespoons of the mayonnaise over them. Bake on the top rack of the oven until the mayonnaise is golden brown, about 10 minutes. Garnish with the green onions and serve hot.
Consumption of raw or undercooked eggs, shellfish and meat may increase the risk of foodborne illness.
Recipe from Every Day's a Party, by Emeril Lagasse, with Marcelle Bienvenu and Felicia Willett, published by William Morrow, 1999