Slice peeled hard boiled eggs in half, placing yolks into a small bowl and the whites onto a plate or serving dish.Mash yolks with a fork.Season with salt, pepper and garlic, if desired.Add in mayo, mustard, onion and pickle relish.Mix until thoroughly combined and taste for seasoning. If you want a creamier mix - add mayo, if you want it to be a bit more tart - add mustard, etc.Spoon or pipe filling into whites.Sprinkle deviled eggs with paprika or cayenne, if desired.Cover and refrigerate until serving. Refrigerate any leftovers.