Preheat the oven to 425°F. Line a baking sheet with aluminum foil and spritz liberally with cooking spray.
In a medium mixing bowl toss together red potatoes, olive oil, chopped rosemary, minced garlic, salt, black pepper to taste and 2 Tbsp grated Parmesan cheese.
Spread in a single layer on the baking sheet. Bake for 30 minutes, turning halfway through until fork tender.
Meanwhile, in a large bowl whisk together the dressing ingredients stirring in the sliced green onions last. Toss potatoes with dressing. Served warm or chilled.
Garnish with additional parsley, Parmesan cheese, red pepper flakes and a sprig of rosemary before serving, if desired.