There are several Kua'Aina branches in Tokyo which I've enjoyed, but not yet in the UK.
Obama's favorite DC hamburger restaurant is Ray's Hell in Virginia (he took Putin there), but it seems to be closed now over a rental dispute.
Chipotle is another US chain moving in around London. The algorithm that what costs $1 in the US costs a pound in the UK, however, doesn't apply as they charge about 15% above that!