Jeremy Meeks is the undisputed rebound champ ... IF the massive rock on his heiress GF's hand is indeed proof he's locked her down.

The felon-turned-model and Chloe Green -- whose father has a $5 BILLION empire -- hit up Nobu Tuesday in Malibu tamely holding hands, and perhaps ... tried to hide her new bling

But Jeremy and Chloe posted a video of themselves all over each other, and Chloe's ring -- which looks awful engagement-y -- was blindingly obvious. It may appear to be on her right hand, but remember it's a selfie so the image is flipped.

The fast lane seems to suit Jeremy. He filed for separation from his wife just last month.