12:21 PM PT -- Jonathan Majors' lawyer Priya Chaudhry tells TMZ ... "This is no surprise. Mr. Majors is preparing counterclaims against Ms. Jabbari."

Jonathan Majors is being taken back to court by his ex-girlfriend Grace Jabbari -- who's now suing him over the assault case ... and some other stuff she claims went down beforehand.

Jabbari just filed suit against Majors ... and in the docs, obtained by TMZ, she's getting into a lot more detail about other alleged instances that she claims occurred before the March 2023 incident that landed him in criminal court, and which ultimately ended with a conviction.

In GJ's lawsuit, she claims the alleged abuse she endured at the hands of Majors started as early as 2021 after they'd started dating -- specifically pointing out a time at the end of that year which she says became the first she started to fear him and his temper ... this after she mentioned a previous relationship, which she says pissed him off and led to a verbal attack.

There are other alleged instances of abuse that she cites -- including a claim that Majors threw her into a shower wall after he got angry with her, while allegedly proceeding to throw objects, like candles and other miscellaneous items.

She goes on to claim Majors assaulted her in London on a number of occasions while he was in town filming "Loki." Jabbari also claims simple things like having company over or laughing on the phone with her mother would anger him and cause him to fly off the handle ... with her alleging he'd smash her headphones, or at times even her head.

Jabbari cites one alleged instance in which she claims that Majors got so angry with her that he slammed her head against a marble floor and even allegedly strangled her.

She claims it was during this time in London that he gave his Coretta Scott King diatribe.

Eventually, Jabbari brings up the incident from March 2023 ... again repeating her claims that he hit her in the car when she tried to look at his phone over a text from another woman.

She goes on to claim that he twisted her fingers in the car, and that when he got out and she followed ... he threw her back in "like a football."

All of this was discussed at length during the trial, and in the end ... the jury convicted Majors over what the jury saw from the evidence outside of the vehicle. Here, however, she's doubling down again in a lawsuit -- insisting he assaulted her in the car and claiming it was the boiling point of what she alleges was a lengthy relationship littered with abuse.

As we reported ... Majors was convicted of misdemeanor assault and harassment in December, and he's currently awaiting sentencing -- even though his team has filed to have the conviction tossed.

Another thing Jabbari is suing Majors for is defamation -- alleging he tarnished her reputation by claiming she lied about the physical abuse during interviews he did pre- and post-trial.

We've reached out to Majors' camp for comment ... so far, no word back.