Peel the hard-boiled eggs and cut them crosswise in half.
Trim a small slice from the bottom of each egg white so the halves sit flat on a serving platter.
Carefully remove the egg yolks and place them in a mixing bowl.
Add the mayonnaise, feta cheese, diced onion, chopped Kalamata olives, and capers.
Mash and mix the ingredients together until the filling becomes smooth and creamy.
Taste the mixture and season carefully with black pepper and salt if needed. Because feta, olives, and capers are naturally salty, only a small amount of additional seasoning may be necessary.
Arrange the egg white halves on a serving plate.
Spoon or pipe the yolk mixture into each egg white cavity.
Garnish with sliced olives, crumbled feta, fresh oregano leaves, and pepper drops if using.
Finish with a light sprinkle of dried oregano before serving.
