Captain reported an APU Fire Indication on push back. The APU auto shut down. The Captain had the aircraft towed back to the gate and deplaned the passengers.

Narrative

After commencing the push back procedure about XA:00 from the gate; we got an EICAS message fire APU; with the associated fire handle illuminated and bottle discharge in the overhead panel. I asked the tow driver to stop the push back. Immediately after the APU shutdown automatically and we lost all electrical power except the battery. The emergency lights came on. I called for the fire APU checklist; which the First Officer (FO) did from the iPad since the screens had gone dark as well. I made a quick PA and then told the tow driver to check the tail for any indication of a fire. When he came back he said he did not notice anything and I told them to pull us back into the gate. The purser then informed me that a passenger had collapsed in his seat. We called the paramedics; who arrived in about ten minutes. We deplaned the passengers through the main cabin door. When the Mechanics were in the flight deck; the fire APU in the EICAS appeared three more times even though the APU had been shutdown for several minutes. The mechanics also said the airplane had a history of having done exactly the same thing five days ago. We performed a parking checklist and left it in the hands of the maintenance personnel.