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 the 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. Cook until fork tender.
Meanwhile, whisk together the dressing ingredients, stirring in the sliced green onions last. When the potatoes are golden and fork tender. toss with the dressing.
This salad may be served warm or chilled. Garnish with additional parsley, Parmesan cheese, red pepper flakes and a sprig of rosemary, if desired.