Preheat oven to 400°F.
Wash and dry potatoes, then cut into halves. Transfer to a medium bowl and add 2 Tbsp of olive oil and Za’atar, then toss to evenly coat the potatoes. Transfer to a roasting pan and roast for 30-35 minutes, until crisp and golden.
While the potatoes are cooking, place the arugula in a large bowl. Add the reserved olive oil, lemon juice and the desired amount of salt and pepper. Toss, ensuring all the lettuce is coated. Set aside.
When potatoes are cooked, remove from the oven and add the potatoes to the bowl of arugula. Add the pickled onions. Serve warm. Enjoy!