Preheat the oven to 350 degrees F and line a pan with parchment paper
Cut the delicata squash lengthwise in half, take out the seeds, then cut into half moon pieces, about 1/3 of an inch thick.
Mix the delicata pieces with the oil, salt and pepper in a bowl to coat evenly. Put the squash in a single layer on the pan and bake for about 25 minutes until soft, and lightly browned around the edges.
While the squash is baking, mix the tahini, lemon juice, parsley, garlic, and water together in a bowl. If the dressing is too thick, add a 1/2 tablespoon of water at a time until the desied consistency is reached.
Use the tahini sauce to drizzle over the roasted squash or as a dipping sauce. Sprinkle with za'atar and parsley to serve.