In small bowl, combine the ham, mayonnaise, mustard, salt and pepper. Spread a generous layer of the ham mixture on each piece of toast. Beat the egg whites until they are firm but not dry. Spoon the whites on the toast. Make a hollow in each portion large enough to hold one yolk. Carefully drop the yolks into the bed of whites. Sprinkle with a little pepper. Place on baking sheet. Bake at 350 for 7-8 minutes or until the yolks are set and the whites are delicately colored. Garnish with parsley. Serve at once.