A quick way is to do the following:
fas3020c1> stats list instances lun
Instances for object name: lun
/vol/esxX_Boot/LUNs/slesx5.lun-C4iRVoX0ZVhf
/vol/esxX_Boot/LUNs/slesx4.lun-C4iRVoWqMs1a
/vol/esxX_Boot/LUNs/slesx3.lun-C4iRVoWqMrwj
/vol/esxX_Boot/LUNs/slesx1.lun-C4iRVoWqMmq7
/vol/esxX_Boot/LUNs/slesx2.lun-C4iRVoWqMrq8
it gives you the unique LUN "id" that is used for stats monitoring, which just happens to be the LUN path followed by the LUN serial, separated by a hyphen.
-Michael