Boil a large pot of water and cook the fusilli pasta according to package instructions. Drain and rinse under cold water to cool the pasta. Shake off excess water and pour the pasta into a large salad bowl.
Add the chopped chicken, tomatoes, scallions, black olives, and cilantro to the pasta.
In a separate bowl, combine the French dressing with sour cream, Old El Paso Taco Seasoning and Chopped Green Chiles. Stir until smooth.
Pour the dressing over the pasta salad and toss well to coat. Toss in the shredded cheese if desired. Cover and chill until ready to serve.
NOTE: Cool Chicken Taco Pasta Salad can be made up to 4 days ahead.