From the off there is one topper unlocked, the 'Portal - Cake'. You can equip it from the Garage under 'Toppers' (See Solution for Grease Monkey In Rocket League
for more details on how to apply)
Once your car is applied with a topper head into exhibition mode and setup a 1v1 match with no bots, which means you'll be playing alone. Now simply score 3 goals and this achievement is yours.
You might also want to try for Solution for Speed Demon In Rocket League