Bring the sun-dried tomatoes and water to a boil over high heat in a small pot. Reduce the heat to low, cover, and simmer for 2 minutes until the tomatoes are soft and the liquid has been absorbed. Set aside and allow to cool to room temperature.
Cook the pasta al dente according to the package directions. Drain, rinse with cool water, and drain again.
Put the cooked pasta in a medium-sized bowl and add the tomatoes, chicken, artichoke hearts, olives, and scallions. Toss to mix. Pour 1/4 cup of the dressing over the mixture and toss to mix. Cover and refrigerate for a minimum of 2 hours.
Place the lettuce in a large bowl. Add the pasta mixture, the remaining dressing, and the walnuts, if desired. Toss to mix. Sprinkle with the cheese and toss again.