In 12 inch skillet, heat I inch water to boiling over high heat.
Add asparagus and 1/2 teaspoon salt; heat to boiling.
Reduce heat to medium low and simmer, uncovered, 5 to 7 minutes until asparagus spears are tender crisp; drain and rinse under cold running water to stop cooking.
Meanwhile, prepare vinaigrette: With vegetable peeler, remove 3 strips of peel (about 3" by 1" each) from lemon.
Slice strips lengthwise into thin slivers.
Squeeze 2 tablespoons juice from lemon.
In small bowl, combine lemon juice with capers, mustard, sugar, pepper, and 1/4 teaspoon salt.
With wire whisk, slowly beat in olive oil until mixture thickens slightly.
Place asparagus in small deep platter.
Pour vinaigrette over asparagus; toss well to coat.
Sprinkle slivered lemon peel on top.