Heat a skillet with the olive oil. Add in the diced onion with a pinch of salt and saute on medium heat for about 10 minutes, until the onions have browned. Stir every couple of minutes.
Mash the hard boiled eggs in a bowl and add in the sauteed onion, harissa, mayo, dijon, parsley and salt & pepper. Mix well.
Serve over toasted bread or with crackers. Leftovers can be refrigerated for up to 4 days.