Make sure your game settings are set to default, but most importantly you have to kill the side turrets in his last form then let him explode by time out. So 1st phase kill the boss, 2nd phase turrets + boss, 3rd phase boss, 4th turrets only and keep dodging for about an eternity, between 3 and 5 mins it seems.
I had trouble unlocking it until I found a comment on 360achievements, tried it and voila. Game was 360 novice by the way.