Place the potatoes in the bottom of a large stockpot.  Fill the pot with cold water until it reaches an inch above the potatoes, then add a tablespoon of salt to the water.

Heat the potatoes over high heat until the water reaches a rolling boil.  Then reduce heat to medium, and simmer for 15-20 minutes, or until the potatoes are fork-tender and cooked through.

Remove from heat and strain out the water.  Then once the potatoes have cooled for a few minutes, remove and discard the potato skins.  Then dice the potatoes into small bite-sized pieces, and sprinkle with the vinegar.  Set aside.

In a large mixing bowl, whisk together the Greek yogurt (or mayo), Dijon mustard and black pepper until combined.

Add the diced potatoes, hard-boiled eggs, avocado, red onion, celery and cilantro to the mixing bowl.  Then very gently toss the potato salad until all of the ingredients are combined and evenly coated with the Greek yogurt sauce.

Garnish with optional toppings if desired.

Serve immediately.  Or cover the salad with plastic wrap so that the plastic is completely touching the top of the salad with no air bubbles, and refrigerate for up to 2 days.  (The avocados may brown slightly after a few hours, but they will still be safe and delicious to eat.)