There have been a couple perspectives on Turan, and some peoples living in Turan like the Sogdians were Zoroastrians. As were other people outside Iran's borders, like the Armenians, who perhaps could have been converted to follow the more orthodox Zoroastrianism of the Sassanid state (or a later Persian state, which would likely include a dynasty of Turkic origins). Same with Georgia and the Caucasus in general, which if Zoroastrianism followed a course like Georgian Christianity (maybe in a Byzantium screw) then Zoroastrianism would eventually move north to the various Caucasian and Turkic peoples there (and the culturally related Alans).
Zoroastrianism is basically the faith of the culturally Persian (not ethnically or linguistically), so as the Persian cultural realm spreads (OTL this includes Turkic countries like Azerbaijan, Uzbekistan, etc.), then so will Zoroastrianism.
As to how you'd get all the Turks to convert to Zoroastrianism, that's a bit trickier, but assuming a strong trans-Caspian trade with the Volga Bulgars plus centers in the North Caucasus like in Alania, then perhaps they might introduce it as their state religion and from there they could convert various steppe hordes that come through the area, and eventually Zoroastrianism becomes the religion of more settled peoples, who by the 16th/17th century perhaps are expanding all throughout Siberia in a manner similar to the Russians. Like Russia, many Turkic groups may not adopt Zoroastrianism, but it will strongly influence their religions regardless. Perhaps this Persian dynasty of Turkic origin would restructure Zoroastrianism in a new manner making it easier to spread.
Armenian is not a good example since by 400 AD the Armenian cruch became a great part of being armenian
Even when the sassanid Shas forced the religion apon them the chrsitian Armenians would revolt or side with Rome
While not as big as Armenian the georgians had also adopted Christianity the Shas forced zoroastrianisim but despite their efforts it never replaced chirstianity
Mepotamia was also largely chirstian
And the sassanid Eastern provinces had many budhist
Well
For it to expand it would need to reform the religion it is also competing against budishim in the east
Considering that the sassanid empire was basically a rump state after the Byzantine sassanid war of 602-628 and the sassanid civil wars of 628-32
If a new dynasty takes control by let's say the time of the Muslims conquest ( that obviously does not happen)
Around 650
The new dynasty would have to first concentrate on internal refrom
Even if you get higly competent men this will take some time to revive the state
It can't expand zoroastrianisim via trade beacuse well trade is dead for this period
Simply put the Caucases are chirstian by 600 AD with the after math of the war and the civil war Persia is in no condition to reclaim these or any territory or expaned via trade
While this is happening Rome would recover sooner and would have trade and the tang dynasty was expanding
This does give Christianity and budishim a head start to convert the turkic tribes
But we'll like I said for the religion to truely expand it would have to refrom
If a turkic state does it when would it do it ?
Some Uyghurs would apdot the religion in starting from 800 AD
Assuming that turkic migrations go the same
The turks could conquer Persia in the mid 10th century
By this time Bulgaria has converted
The magyars are on there way
Same as the Rus
(Note with a stronger byzantuim the magyars and Bulgaria could convert faster)
So yeah for the western steppe Christianity has more advantages
Volga bulgaria could be chrsirian with out Islam
An area where I can see zoroastrianisim beging to expand is trasoxiana