1. Combine first 7 ingredients in a small bowl, stirring with a whisk. Gradually add olive oil, stirring well with a whisk.
2. Steam asparagus, covered, for 3 minutes. Drain and rinse under cold water; drain. Arrange 2 prosciutto slices in the center of each of 4 plates. Arrange asparagus spears evenly over prosciutto.
3. Add water to a large skillet, filling two-thirds full; bring to a boil. Reduce heat; simmer. Break eggs into each of 4 (6-ounce) custard cups coated with cooking spray. Place custard cups in simmering water in pan. Cover pan; cook 10 minutes. Remove custard cups from water, and carefully remove eggs from cups. Arrange 1 egg over each serving, and drizzle with about 1 tablespoon dressing. Sprinkle each serving with 1 teaspoon chives, if desired.