Bring a large pot of lightly salted water to a boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain and rinse with cool water. Pour into a large dish.
Combine mushrooms, olives, celery, onion, cheese, corn and green bell pepper with pasta; mix well.
In a small bowl, whisk together dressing and mayonnaise; pour dressing over salad and toss again to coat.
Gently mix in flaked chicken; refrigerate for a few hours or serve.