Place eggs in a small saucepan with enough cold water to cover by 1 inch (2.5 cm); bring to a boil over high heat. Immediately remove from heat; cover and let stand for 16 minutes. Drain and return eggs to pan; cover eggs with cold water and let stand until cool. Drain and peel.
Shallot Tarragon Vinaigrette: Meanwhile, in a bowl, whisk oil, vinegar and mustard. Add salt and pepper, to taste. Stir in shallot and tarragon.
In a large wide saucepan of boiling salted water, cook asparagus until tender-crisp, about 2 minutes. Drain and chill in cold water. Drain well and pat dry.
Cut eggs in half; separate yolks from whites. Using a grater, coarsely grate whites into a small bowl and yolks into another.
When ready to serve, line a serving platter with watercress. Gently coat asparagus with half of the vinaigrette; arrange on watercress. Sprinkle with egg whites, then egg yolks. Drizzle with remaining vinaigrette.
Per serving: 143 calories, 5 g protein, 12 g fat (2 g saturated fat), 5 g carbohydrates, 2 g fibre, 106 mg cholesterol, 53 mg sodium