1. In a large frying pan, bring the water and 3/4 teaspoon of the salt to a boil. Add the shrimp, cover, and bring back to a boil. Cook, covered, over moderate heat for 1 minute. Stir. Continue cooking until the shrimp are just done, about 2 minutes longer. Drain. When the shrimp are cool enough to handle, cut each one in half lengthwise and then in half crosswise.
2. Put the shrimp in a large glass or stainless-steel bowl and add the jicama, mango, and cilantro.
3. In a small glass or stainless-steel bowl, whisk together the lemon juice, the mustard, the remaining 1 1/4 teaspoons of salt, and the pepper. Add the oil slowly, whisking. Just before serving, add this vinaigrette to the shrimp mixture and toss.
Shellfish Alternatives : Crabmeat, though expensive, is delicious in this salad and is a time-saver, too, since it's usually already cooked. (For that matter, you can use precooked shrimp instead of boiling uncooked ones.) If you really want to splurge, try the salad with lobster.
Wine Recommendation: Mango, lemon juice, and cilantro invite a light-bodied, acidic white, such as an Orvieto from Italy or a Muscadet de Sèvre-et-Maine from France.