Cook your pasta in salted boiling water just until tender, slightly softer than al dente. Once done, drain and rinse it under cold water to stop cooking and wash off extra starch.
In a bowl, whisk together lemon juice, lemon zest, white balsamic vinegar, Dijon, salt, pepper, capers, and chopped walnuts. Slowly drizzle in the olive oil until everything is well combined.
In a large bowl, add the cooled, rinsed pasta and gently toss in the lemon dressing. This will allow each piece of orzo to get coated with the bright, tangy dressing.
Finally, toss in the fresh arugula. The arugula will wilt slightly if the pasta is still warm but it will absorb all the citrusy flavors from the dressing.
