Combine potatoes, oil, rosemary, 1/2 teaspoon salt, and 1/2 teaspoon pepper, tossing gently, and spread in a 15- x 10-inch jelly-roll pan coated with cooking spray.
Bake at 400° for 40 to 50 minutes or until potatoes are tender and lightly browned. Sprinkle evenly with 1/4 teaspoon salt and 1/4 teaspoon pepper; keep warm.
Cook bacon in a large skillet until crisp; remove bacon, and drain on paper towels, reserving drippings in skillet. Crumble bacon, and set aside.
Whisk vinegar, next 3 ingredients, remaining 1/4 teaspoon salt, and remaining 1/4 teaspoon pepper into skillet; cook over medium heat, whisking occasionally, 3 to 4 minutes or until thoroughly heated.
Combine spinach and mixed greens; drizzle with warm dressing, tossing to coat. Top with potatoes, bacon, and Parmesan cheese; serve immediately.