Preheat the oven to 450 degrees Fahrenheit. Line a rimmed baking sheet with parchment paper and add the potatoes on top.
Drizzle the potatoes with olive oil and season well with kosher salt and fresh cracked pepper. Use your hands to toss the potatoes on the sheet to coat evenly with the oil and seasoning. Spread them out evenly on the baking sheet and place in the oven to roast for 20 minutes.
Meanwhile, make the mustard vinaigrette. In a small bowl, whisk together the extra virgin olive oil, mustard, garlic, and oregano.
When the potatoes are done (they should be tender when pierced with a fork and slightly golden) transfer them to a large serving bowl and pour the dressing over top. Toss to coat, taste them, and season as needed with extra salt and pepper. Enjoy right away while still warm!