Cook orzo pasta according to instructions in salted water. When pasta is al dente, reserve some of the pasta cooking water, drain and rinse the pasta with cold water.
In a small food processor, combine the jarred sun-dried tomatoes plus any oil in the jar, garlic, lemon juice, and walnuts. Pulse until mixture is in a rough paste.
Stir sun-dried tomato mixture into the orzo. If the mixture seems dry, add pasta water by the 1/4 cup until it smooths out.
Finally, fold in fresh arugula and parmesan cheese. Taste and season with salt and pepper to your liking.
Serve at room temp or chilled. Leftover pasta salad will keep great for 4-5 days. If you are storing for more than 24 hours, leave out the arugula until you are eating it so it doesn’t get too wilted.