In a salad bowl whisk together the tahini and lemon juice until smooth. Slowly add water, whisking constantly until smooth. Whisk in salt.
Add all ingredients except for olive oil (cucumber through mint) and toss gently to coat evenly. Cover and refrigerate for 30 minutes to let the flavors meld.
When ready to serve, gently toss once more then drizzle with olive oil and, if desired, divide among 4 bowls. Serve.