In a jar with a tight-fitting lid, combine the vinegar, soy sauce, 1-1/2 teaspoons oil, sugar and garlic; shake well and set aside. In a large nonstick skillet, saute the onion, peppers and mushrooms, in 1-1/2 teaspoons oil until tender. Remove and keep warm. In same skillet, saute chicken in remaining oil until juices run clear; drain.
In a large bowl, combine the pasta, lettuce, oranges, olives, onion mixture and chicken. Pour dressing over lettuce mixture; toss to coat. Serve immediately. Yield: 6 servings.