Cut the hard boiled eggs in half lengthwise and set aside the yolks in a mixing bowl.
Mix the yolks with mayonnaise, ketchup, and mustard until smooth and then season with salt and pepper. Spoon the mixture into a piping bag.
While heating the oil, dip the egg whites in flour, beaten egg, and then breadcrumbs. When the oil is hot, fry the breaded egg whites until golden brown.
When cooled slightly, pipe the yolk mixture into the indentation of the fried egg whites.