Whisk first 3 ingredients and 1 tablespoon mint in small bowl; whisk in oil. Season dressing to taste with salt and pepper. Toss greens with 2 tablespoons dressing in medium bowl; divide between 2 plates. Place melon next to greens; drape prosciutto over melon. Drizzle remaining dressing over prosciutto and melon. Sprinkle with remaining 2 tablespoons mint and freshly ground pepper and serve.