Bring a large pot of water to a boil. Add two tablespoons of salt.
Cut the potatoes into quarters and then cut each quarter into chunks that are roughly one inch big. Add the potatoes to the boiling water and let cook until potatoes can be easily pierced with a fork, about 8-10 minutes.
While the potatoes cook, whisk together the tahini, warm water, oil, lemon juice and lemon zest in a large mixing bowl. Season with 1 teaspoon of salt and ½ teaspoon of pepper.
Drain the potatoes. While the potatoes are still hot, add them to the dressing and toss. Add in the celery, onion, chopped celery leaves and parsley. Place in the fridge and let chill for at least an hour before serving.
Right before you serve the potato salad, add in the arugula and toss. Can be served cool or at room temperature.
Grant Melton is an Emmy Award-Winning Producer of the Rachael Ray Show, food writer and recipe developer. He's a contributor to Food52, Food Network Kitchen and Rachael Ray Every Day Magazine. His favorite food is chocolate chip cookies (with salt.)