Peel hard-boiled eggs and slice them in half lengthwise. Scoop out the yolks and place in a small bowl, along with mayo, mustard, onion powder, salt, pepper and cayenne pepper (if using).
Use a fork to mash the mixture together. Place the egg white halves hole-side up on a serving plate and spoon or pipe the yolk mixture into the holes.
Sprinkle with paprika and refrigerate until ready to serve.
Hummus: Add a few tablespoons of hummus to the yolk mixture in place of mustard, as well as a few splashes of fresh lemon juice.
Spicy: Add a few splashes of Tabasco sauce (or your favorite hot sauce) as well as some diced jalapenos.
Guacamole: Replace the mayo and mustard with 1/2 of an avocado, 3 tablespoons sour cream and a few squirts of fresh lime juice. Replace the paprika with cayenne pepper.
Buffalo: Replace the mustard with an equal amount of buffalo sauce. Finely diced celery (about 1/4 cup) can be thrown in, too! Omit paprika.
Meat Lovers: Add up to 1/2 cup chopped meat such as bacon, turkey, chicken, ground beef or ground sausage.
Fish Lovers: Add 1 small can of drained tuna fish or 1/2 cup cooked, flaked salmon.
Herbed: Load the mixture up with chopped herbs such as chives, parsley, cilantro, basil or thyme.