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 in cold water.
In a large bowl, combine pasta, green capsicum, red capsicum, onion, celery, olives and prawns. In a separate bowl mix together salad dressing, mustard, sugar, vinegar, salt and pepper; pour over salad. Can be served immediately, but best when chilled a few hours.