Hi,
There is an excellent guide on the oracle site
here - - as I read it (but I've been known to be wrong). I can't really understand the logic of a single disk in a zpool, as there are no data replicas available that allow the benefits of zfs - you might as well use UFS at least you have more recovery tools.
Obviously the best approach would be to grow the original LUN or have the SAN admin people do this, then grow the FS into it. In any case you should ensure that you have a backup of the data before you start doing anything.
Regards
Gull04