Place potatoes in a large saucepan; add water to cover by 2 in. Bring to a boil. Reduce heat; cook, uncovered, until tender, 10-12 minutes, adding asparagus during the last 2-4 minutes of cooking. Drain potatoes and asparagus; immediately drop into ice water. , To serve, drain potatoes and asparagus; pat dry and divide among 4 plates. Add tuna and, if desired, olives. Drizzle with dressing.