1. Whisk all dressing ingredients until smooth and set aside. 2. Brush the sliced pita with 1 tablespoon olive oil and grill or toast; set aside. 3. In a bowl, toss together remaining 2 tablespoons olive oil, chickpeas, scallions, tomato, za’atar, harissa, cumin, lemon juice and parsley and season to taste. 4. Spoon the mixture on top of the pita slices, drizzle with the tahini sauce and serve immediately.