Zarthastno Diso

This is the day on which the followers of Zoroaster (or Zarathushtra), the Persian prophet and religious reformer, commemorate their founder's death, at one time believed to have occurred in 551 b.c.e. He is now believed to have lived around 1200 b.c.e. Zoroaster was a figure associated with occult knowledge and the practice of magic on the one hand, and on the other, with the monotheistic concept of God familiar in modern-day Christianity and Judaism. The largest group of his followers are the Parsis of India, although they can also be found in isolated areas of Iran, and elsewhere around the world.
Zoroaster's death is observed in April by the Fasli sect of Zoroastrians, in May by the Kadmi sect, and in June by the Shahenshai sect.

SOURCES:
RelHolCal-2004, p. 69