In a large skillet cook zucchini, asparagus, green onion, and peas in hot oil over medium heat for 3 to 5 minutes or until asparagus is just crisp tender, stirring occasionally. Transfer to a medium bowl; cover and chill for 2 to 24 hours.
In a large bowl toss together arugula and watercress. On two dinner plates. Stir salsa and vinegar into chilled vegetables; spoon over greens.