Preheat the oven to 425 degrees F. Put the olive oil, lemon juice, shallot, garlic, oregano and parsley in a food processor; add 1 teaspoon salt, and pepper to taste. Puree until mostly smooth.
Toss the potatoes with 1/2 cup of the prepared vinaigrette in a large bowl and spread in a single layer on a large rimmed baking sheet. (Reserve the remaining vinaigrette.) Roast the potatoes until tender and golden, turning occasionally, 45 minutes to 1 hour.
Transfer the potatoes to a platter and drizzle with some of the remaining vinaigrette. Season with salt and garnish with the chopped parsley. Serve with the remaining vinaigrette on the side.