In a small bowl, whisk together all of the herbed yogurt sauce ingredients until smooth. Set aside.
In a large bowl, combine shredded chicken, avocado, cucumber, onion, and cherry tomatoes. Add half of the yogurt sauce and toss gently to coat.
Lay out 8 lettuce leaves. Spoon chicken mixture evenly into each leaf. Drizzle with remaining yogurt sauce and sprinkle with 2 Tablespoons chopped walnuts for extra crunch.
Notes
These wraps taste best fresh, but you can make the filling ahead of time. Place the filling and walnuts in the lettuce wraps when ready to serve.