Drain pineapple, reserving 1/4 c. juice; set pineapple aside. Combine reserved juice, vinegar, soy sauce, oil, & gingerroot in a small bowl. Stir well, cover & chill.
Place snow peas in a steamer over boiling water. Cover & steam 1 min. or until crisp-tender. Rinse with cold water, drain & set aside.
Place carrots in steamer over boiling water. Cover & steam 3 min. Rinse with cold water; drain & set aside.
Line a large serving platter with watercress. Arrange pineapple, snow peas, carrots & bell peppers attractively over watercress. Cover & chill. To serve pour vinegar mixture over salad; sprinkle with sesame seeds.