Place potatoes in a large pot of water and bring to a boil. Cook until fork tender and remove from heat, drain and set aside in a bowl.
While the potatoes are cooking, place the pancetta in a large skillet over medium-high heat. Fry until browned and crisp, turning as needed. Remove from the pan and set aside.
Add the diced onion to the pancetta grease, and cook over medium heat until browned.
Carefully add the vinegar and mustard to the onions and cook for 2 minutes and turn off the heat. Whisk in the oil and season, to taste, with salt and pepper. Add the hot dressing to the potatoes and toss gently to coat. Fold in the pancetta, green onions, chives, and parsley. Season with salt and pepper to taste.