After you defeat your future self and then your custom avatar (if you choose not to shoot your future self), you can return to the menu and then go back into the present world to find a dragon in the parking lot in front of you.



Get on it, fly over to the basketball court, and breath fire all over the cows. They will turn into hamburgers.



You can also do this to the giant cow(s) in either the present or future. They both count towards the achievement.



Good luck.