What has Abraham got to do with it? He pre-existed Zoroaster!
That's not necessarily the case, assuming that Abraham even existed. Zoroaster may not be a credible historical figure either.
And how do you know that Abraham pre-dated Zoroaster?
Zoroaster in the estimation of the Greeks, lived some 6,000 years before their time, or 8,200 to 8,500 years ago. Pliny the Elder (AD 23-79) quotes Eudoxus of Cnidus (ca. 365 BC) and Aristotle (ca. 350 BC) as placing Zoroaster 6000 years before the death of Plato (347 BC) or
6365 BC. Pliny also quotes Hermippus (ca. 250 BC) as placing Zoroaster 5000 years before the Trojan war (ca. 1200 BCE) or around
6200 BC. Diogenes Laertius (AD 230) states that according to Xanthus of Lydia (ca. 450 BC), Zoroaster lived 6000 years before the Persian king Xerxes invaded Greece (ca. 480 BC) or about
6480 BC. Diogenes also states that according to Hermodorus (ca. 400 BC), a follower of Plato, Zoroaster lived 5000 years before the Trojan war (ca. 1200 BC). Plutarch (ca. AD 46-120) also places Zoroaster 5000 years before the Trojan war.
These dates for Zoroaster may be wildly inaccurate, however the Bible's internal chronology for the dating of Abraham also cannot be relied upon.
The late Mary Boyce (1920-2006), Professor of Iranian Studies at the University of London, stated in her book
Zoroastrians, Their Religious Beliefs and Practices that "to hazard a reasoned conjecture" was "that Zoroaster lived sometime between 1700 and 1500 B.C.
The Abrahamic religions pre-exist Zoroaster who could have been born within about an 800 year span according to 'scholars'.
And how do you know the Abrahamic religions began with an individual called 'Abraham'? Through the Deutronomist, Priestly and Jahwist writers of the 6th and 5th centuries?
You claim, for want of a better term, tampering with the texts of the biblical scriptures, but the Avesta is from the 300's AD and the earliest manuscripts? 13th century.
The vast majority of scholars, including Mary Boyce who wrote
Textual sources for the study of Zoroastrianism (published in 1984) and Peter Clark,
Zoroastrianism. An Introduction to an Ancient Faith (published in 1998) agree that the Avesta is much older than AD 300. For example, They agree that the seventeen Gathas, possibly composed by Zoroaster himself, are the oldest part of the Avesta. The language of these hymns resembles that of the Indian
Rigveda, hymns that were most likely composed in the Punjab between 1500 and 1200 BC. For example, the Gathic word
ahura, "divine lord", is virtually identical to the Vedic word
asura.
The bulk of the Avesta was almost certainly written before the Parthian period. (c. 247 BC) (That there was a large religious literature, can be deduced from a remark by the Roman author Pliny the Elder who wrote about the Alexandrine scholar Hermippus of Smyrna (third century BCE):
"Hermippus, who wrote most painstakingly about the whole art of magic and interpreted two million verses by Zarathustra, also added lists of contents and handed down the name of Agonaces as the teacher who instructed him, placing Zarathustra [Zoroaster] five thousand years before the Trojan War."
As I said, Darius I (550-486 BC) was a devotee of Ahura Mazda as attested to several times in the Behistun inscription, indicating that Zoroastrianism was well established during the Jewish exile in Mesopotamia
Now put on your critical of christianity cap
I'm not speaking of Christianity in this case. I'm speaking of Judaism.
and apply the same tests you use to disprove the bible, and place them on those texts and tell me who may or may not have added and subtracted from which texts and who may have influenced the other.
I've already explained in detail how and why some aspects of the theology of Judaism were influenced by Zoroastrianism. Re-read it.