What is the average fastest lap time in seconds for Lewis Hamilton in all the Formula_1 races?
average fastest lap time = avg(fastestLapTime); The time is recorded on 'MM:SS.mmm'
SELECT AVG(CAST(SUBSTR(T2.fastestLapTime, 1, INSTR(T2.fastestLapTime, ':') - 1) AS INTEGER) * 60 + CAST(SUBSTR(T2.fastestLapTime, INSTR(T2.fastestLapTime, ':') + 1) AS REAL)) FROM drivers AS T1 INNER JOIN results AS T2 ON T1.driverId = T2.driverId WHERE T1.surname = 'Hamilton' AND T1.forename = 'Lewis'