1. Combine first 3 ingredients in a small bowl, stirring with a whisk. Place spinach in a large bowl. Drizzle with half of oil mixture. Add pepper; toss well to coat.
2. Arrange prosciutto slices evenly on each of 6 salad plates. Top each serving with 1 cup spinach mixture. Drizzle evenly with the remaining oil mixture. Sprinkle each serving with 2 teaspoons cheese. Serve immediately.