In a large bowl, toss potatoes with oil and salt. spread in a single layer on a baking sheet and roast in a preheated 425 degree oven for 40 to 45 minutes or until browned, crisp and tender.
Meanwhile, to prepare dressing, in a large bowl combine vinegar, garlic, salt and mustard.
Whisk in oil. Stir in parsley.
Add hot potatoes to dressing and toss.
Serve warm or at room temperature on a bed of arugula or mustard greens.