Whisk olive oil, lemon juice, shallots, garlic, oregano, and parsley in a medium bowl to blend; season with salt and pepper.
Toss potatoes with 1/2 cup vinaigrette on a heavy, large, rimmed baking sheet. Reserve the remaining vinaigrette. Pour chicken stock around potatoes and season potatoes with salt and pepper. Roast potatoes until tender and golden brown, turning occasionally, about 45 minutes. Transfer to a serving platter and drizzle with the remaining vinaigrette and more chopped parsley.