What is the average score of Lewis Hamilton among all the Turkish Grand Prix?
Average score = AVG(points)
SELECT AVG(T2.points) FROM drivers AS T1 INNER JOIN driverStandings AS T2 ON T1.driverId = T2.driverId INNER JOIN races AS T3 ON T3.raceId = T2.raceId WHERE T1.forename = 'Lewis' AND T1.surname = 'Hamilton' AND T3.name = 'Turkish Grand Prix'