Peel the eggs and halve them lengthwise, then place 1 egg yolk in a small bowl; discard the remaining yolks.
With a fork, mash the yolk; then add 4 of the egg white halves and mash them.
Mix in the green onion, mayonnaise, parsley, pickles, mustard, salt, and pepper.
Mound the mixture into the remaining egg white halves, dividing it evenly.
Garnish each half, if you like, with a parsley sprig.
Cover loosely and refrigerate until ready to serve.