To a pot over medium heat, boil the eggs for 10 minutes until well cooked, then peel. Dice the celery and chop the parsley. In a medium bowl, smash the hard-boiled eggs with the back of a fork. Stir in the yogurt, celery, parsley, Dijon mustard, pepper and salt.
Step 2
Cut the cucumber in half crosswise, then cut each piece in half lengthwise. With a small spoon or measuring spoon, scoop out and discard the seeds.
Step 3
Divide the egg mixture evenly between the four cucumber boats. Sprinkle with cayenne, if desired. Serve.