Start a Grand Prix of 20% distance, any track. Choose either Red Bull, McLaren or Ferrari and change the difficulty to easy. To lap a car, you must overtake them when they are on a different lap (less than the one you are on). With the AI being around 10 seconds slower on average (on easy) you should start lapping them after 7-8 laps. Simply lap 6 cars before the race finishes to be awarded the achievement.
If you have a lot of spare time and wish to make it easier on yourself, set the distance to 50% instead of 20%.