Hold the back button and open up your keys to the city menu. Click spawn objects. Click explosive props. Tap up on the DPad. Spawn 20-30 small fuel tanks. I did 30 just to be sure. Then go back into your menu and spawn a grenade launcher. Shoot one of the tanks and this achievement is yours.
Edit: I'm sure you can just use any weapon and shoot one fuel tank but if you're going to complete this DLC in 30 mins, may as well have fun doing it. Right?
Another helpful tip, thanks Death:
I spawned 6 vehicles around the fuel tanks to get the pile up achievement at the same time.