Wash and clean potatoes. Cut into 1" cubes and place in a pot full of water and bring to a boil. Cover and cook over low-medium heat for 25 minutes. Potatoes should be tender when pierced with a fork, not falling apart. Drain and rinse with cold water.
To make salad dressing, combine the oil, vinegar, garlic, mustard, 1/2 tsp salt and black pepper in a small bowl. Whisk with a fork until well combined.
Place cubed potatoes in a large bowl and stir in chopped onions and parsley, mixing well. Add the salad dressing and mix well. Chill potato salad for about one hour and serve. Makes 6 servings.