1:25 PM PT -- We just got video of the incident ... and you see Miranda's millennial friend getting screamed at by the guy whose wife ended up with a salad on her lap. The video was shot after Miranda dumped the salad on her.

The last part of the video shows Miranda walking out of the steakhouse.

And, check out the photos ... in one you see Miranda being held back by her millennial friend ... that's how heated it got.

Postscript ... we found the salad in question was NOT Miranda's. Turns out the singer grabbed the salad the woman was eating and rearranged it on her lap!

Miranda Lambert had a heated exchange with a couple dining at a Nashville steakhouse, and things got so nasty she dumped a salad on a woman she says was provoking her ... TMZ has learned.

Sources close to Miranda say the food fight went down Sunday night at Stoney River Steakhouse, where the singer was dining with her mother and a family friend. We're told an older man started beefing with Miranda's buddy, and things started spiraling out of control.

Law enforcement sources tell TMZ ... cops responded to a call about 2 men fighting, but by the time police arrived at the scene, Miranda and her party were gone. We're told cops didn't file a report.

As for why Miranda felt compelled to dump her dinner on the woman ... we're told the woman's husband picked a fight with Miranda's friend, which started in the men's restroom with a wisecrack about millennials and their phones.

Eyewitnesses say Miranda had to be held back after the man came up to her table and started screaming ... we're told Miranda started mouthing off and eventually walked over to the man's wife, got feisty with her and dumped a salad in her lap!!!

We reached out to Miranda's team, they had no comment. We also reached out to the restaurant's corporate office ... so far, no word back.