In a small bowl stir together raspberry vinaigrette and tarragon; cover and chill until serving time.
Remove strings and tips from peas; halve peas diagonally. In a medium saucepan cook peas in boiling water for 1 minute; drain. Rinse with cold water; drain again.
Halve cantaloupe; remove seeds and peel. Using a mandoline, cut cantaloupe into thin slices. Arrange peas, cantaloupe, and watercress on a platter. Drizzle dressing over salad and sprinkle with almonds.