For sauce, combine in a bowl yogurt, mayonnaise, mustard, lemon juice and salt. Whisk until smooth and set aside.
Bring water to a boil in a 12-inch skillet over high heat. Add asparagus, return to a boil, reduce heat, cover tightly and simmer 3 minutes or until just tender crisp. Remove from water and drain on paper towels.
Place asparagus on serving platter and spoon sauce over all. Sprinkle with black pepper.