I tried few times now. Not too much practice, but my facit:
Passing two cars is not so difficult, one way is squeezing inbetween them before or during the first turn. But it needs a bit luck not to hit another car, or be hit by them.
Because just being quick is not enough, you also have to drive in a way that is compatible with the AI drivers. For example on the straight they always seem to drive very far to the right side after the bridge, even if you are beside them. Other times they brake very early if you beside them, might be possible to exploit that.
I did not manage to pass the third car. Sometimes it was close, or I was already past, but then got contact and lesson failed.
Passing on the long straight I found difficult, because the exit speed depends on how much the other cars hindered you.
In the "2nd" replay I passed two cars in usual way in T1, then waited until end to pass at the last turn/finish. That seemed most promising strategy but never worked.
Maybe the purpose of this lesson is that it requires luck to pass three cars in one lap.