Cook fettuccine according to package directions, omitting salt and fat. Drain and rinse under cold water; drain again. Set aside.
Cook broccoli, carrot, and celery in a small amount of boiling water 6 minutes or until crisp-tender. Drain; plunge into ice water, and drain again.
Combine cooked fettuccine and broccoli mixture in a large bowl. Combine Italian dressing and next 3 ingredients; stir well. Add to fettuccine mixture; toss gently. Stir in chicken and tomato.