Boil the potatoes for 20- 30 minutes until there can be easily pierced with a fork. Drain and allow to cool. Peel the skins from the potatoes.
Cut the potatoes into 1/2 square pieces, sprinkle with vinaigrette.
Mix with the onion,tomatoes add the mayonnaise and fold into the potato mixture and season with salt and pepper to taste. Sprinkle with chopped parsley.
Chill for at least 1 hour before serving
Notes
If you are trying to cut some fat in your diet you can use plain yogurt.