Here are two verses of Zarathustra from his Gathas published in the The Hymns of Zoroaster: A New Translation of the Most Ancient Sacred Texts of Iran by M. L. West:
And that reward, Mindful One
Thou dost keep in your house
Good thought, and the souls of the Righteous
And Reverence, with which are Piety and Libation
Besides ... that confer lasting Dominion
But as for the ill-dominioned, ill-actioned, I'll-speaking, ill-moralled, ill-thinking wrongful ones
The souls come to them with foul food
In the house of Wrong they will be veritable lodgers
They seem to be rather (!) at odds with Nietzschean philosophy, and Zarathustra did not speak in the way that Niezsche said he did.
Q. What evidence is there that Nietzsche was both familiar with Zarathustran philosophy and understood it?