Remove the cooked egg yolks and place in a small bowl.
Add mayonnaise, mustard, and onion powder.
With a small hand mixer, combine ingredients until smooth.
Refrigerate for 10-15 minutes.
Next, arrange cooked egg white shells on a serving dish.
Place egg yolk mixture into an icing bag with a small tipped spout.
Fill the egg white shells with yolk mixture.
Garnish, as desired. If not serving immediately, cover lightly with plastic wrap and refrigerate for up to one day.