Peel the eggs and slice the eggs in half longwise. Place the egg whites on a plate or serving dish.
Put the yolks in a sealable plastic bag with the onions, olive oil and spicy mustard. Squeeze out all the excess air and then seal the bag.
Squish the bag with your fingers to mix all the ingredients. When the yolk mixture is blended and creamy, cut a small triangle from the bottom corner of the bag.
Use the bag as you would use a pastry bag to squeeze the yolk mixture into the egg whites.