FGCM is highest level of court martial. It is sanctioned by parliament under Armed Forces Act 1973 and gives power to Army, Navy and Air Chief to give death penalty. Act applies to Armed Forces personnel but can be applied to only those civillians which indulge in attacking with criminal force against military personnel and installation and captured by Armed Forces. Any punishment thus awarded can not be carried out by Armed Forces but by civil authorities.
Similar law with similar powers exists with Indian Armed forces, I believe. It is as per law of Pakistan.
Given the ban on execution of death penality, there wasn't much point in awarding it. They were rather kept locked till now.