Hard-boil the eggs by placing them in a pot of cold water, bringing to a boil, then simmering for 10 minutes.
Cool the eggs under cold running water or in an ice bath. Peel them carefully and slice them in half lengthwise.
Remove the yolks and mash them in a bowl.
Add the chopped chicken, mayonnaise, yogurt (or cream cheese), and mustard to the mashed yolks. Mix until smooth.
Season the mixture with salt and pepper to your liking.
Spoon or pipe the filling back into the egg whites.
Sprinkle chopped parsley or chives on top for a little color and fresh flavor.
Serve chilled or at room temperature.