I recall a construct your own MOS burger kit on a Y flight on JAL It was curiously diverting.

There are some great burgers in the UK. My favourites are the now I think sadly defunct Troll's Pantry in Brighton, these were available rare, from a little hut underneath the station latterly, and made with absolutely the best foraged and artisan extras you won't now ever taste, because he disappeared somewhere. Where many burgers, including the late BA burger (now off the CCR menu too I understand) leave you struggling for air after half a patty and bun, a Troll Burger would leave you in the queue for another.

A strong second would be Burger Off in Hove.