In order to unlock this achievement you must simply earn a gold medal on the track Long Beach Full Circuit in career, multiplayer and free play. In order to get a gold medal, you have to place top three in career, first in multiplayer, and depending on how many A.I. you set in free play, either first or top three. I would suggest finding a series you’ve already completed in career so you can scroll through the different races in that series to find this specific track (Each series should have one race on Long Beach Full). For free play, I suggest setting the game to at least 7 racers including yourself (6 A.I. players), and 2 laps to make the race go by quick, but still allot yourself enough time to claim first place. To nab the multiplayer medal I suggest finding a boosting partner, and setting the game to 6 players total, you, your partner, and 4 A.I. players, again setting the race to 2 laps to be able to scoot into first with enough time.
Note, these three gold medals need to be earned on the Long Beach Full Circuit, you cannot unlock this achievement by driving on either of the two shorter Long Beach tracks.
I hope this solution helped! Leave a comment letting me know if there is any room for improvement! Thanks.