Heat a small saute pan over medium heat. Add the olive oil and garlic and cook just until fragrant, 2 minutes. Allow to cool slightly. In a large bowl, whisk together the tahini and lemon juice. Gradually whisk in the garlic oil. Add the kale, salt and chickpeas and gently toss together, bringing the dressing up from the bottom to coat everything evenly. Add the chicken and cranberries, and toss. Sprinkle with za'atar if desired. Serve.