Rinse rice in a fine wire-mesh strainer. Bring 1 1/2 cups salted water to a boil over medium-high heat in a small saucepan. Stir in rice, and return to a boil. Reduce heat to low; cover and simmer, stirring occasionally, 40 to 50 minutes or until tender. Drain rice, and rinse under cold water; drain. Stir together chicken, next 3 ingredients, and rice in a large bowl until combined. Drizzle desired amount of Tarragon Vinaigrette over salad; toss to coat. Chill 1 hour. Toss with watercress and desired amount of remaining vinaigrette before serving.