You get a 'Chicken Dinner' by being the last man standing, in this case in a solo game of PUBG.
I however was able to unlock it by playing around in the new Training Mode and 'playing' until the 30 minute session ended. All the times I have played in it until the session end, I was shown as #1, so I'm not sure if there is any 'criteria' for being given #1 spot, but by the time the session had ended, I was the only player not AFK.
EDIT: You don't need to be active or the last man active, simply be at the end of the session and the achievement to unlock. Thanks to starofdavid11 and BiLLzuMaNaTi for confirming.
EDIT 2: As of 7/11/18, this has now been patched. Thanks to El Diablo Queso & Sashamorning for confirming