So obviously the dish is kind of a fluid thing, but here are my observations.

My wife, who is a native speaker of Mandarin, has never heard of Za Jiang Mian. It is always Zha Jiang Mian. I suspect people drop the "h" not realizing that "Zh" in pinyin is more like a "j" sound.

Second, this dish, in China, is not typically prepared with doubanjiang (though I am sure people have done it) which is a paste that includes fava beans. Instead it is made with tianmianjiang, a sweet soybean/flour paste not dissimilar to hoisin. A very popular variation that I prefer adds yellow bean paste.

The Korean version uses chunjang, fermented black soybeans. It is pretty similar to tianmianjiang.

I find the Korean version typically a bit overkill on the sauce and one-dimensional, though still satisfying. I like the mix of tianmianjiang and yellow bean sauce that cuts the sweetness a bit.

In neither version are the noodles stir fried, but instead boiled in water separately and then topped with sauce. However, much like Italian pasta, I believe the best results are achieved by finishing the cooking of the noodles in the sauce with a bit of noodle cooking water.

In the US, I've only had this dish at Great Seas and Han Bun. A Korean friend of mine tells me its a ubiquitous dish served at Korean-owned Chinese restaurants. In Beijing, this is the most popular noodle dish in town, and indeed it was very different than what I've had at Great Seas and Han Bun. I posted pics of a couple versions in this thread.

So I talked to my wife and she says there is a similar Za Jiang Mian dish that originates from Sichuan. Looking at recipes revealed that it feature ya cai and doubanjiang and/or yellow bean paste, that is it will not have any sweetness.

As for restaurant recommendations, I like Slurp Slurp's rendition in Cermak. Oiistar puts out a frankly ridiculous and not at all traditional take on the Korean dish that I enjoy. Ahjoomah's Kitchen in Chinatown is a pretty standard Korean version. I cant comment on Great Sea or VIP as they are a bit out of my geographic range.