From the main menu, select Quick Play with
. Choose the following options:
Game mode: Destruction
Location: Lion's Stadium
Opponents: Any (they're only there for the leaderboard)
You won't be able to set the number of laps or the AI difficulty as they're not needed for destruction. Resets don't matter as you shouldn't need them.
My video below shows an easy path to hit a x30+ combo. Be sure to drive slowly over the rows of cars so they all count, and don't forget to steer with the rear wheels for tighter turns. Aside from that, follow my line and try not to go any slower than I did and you should be able to get this very easily. The achievement will unlock on the results screen after the event is finished.