The Duke and Duchess of Sussex hit the town Friday in Santa Barbara, where eyewitnesses say it was just the two of them as they exited a restaurant called Sushi Bar ... a stone's throw away from where they live in Montecito. Of course, some security was in tow.

As you can see, the couple was all smiles as they left the establishment -- and we're told they turned the corner to get inside a waiting SUV that was parked near the adjacent Montecito Inn, at which point they took off. Our sources say this was around 7 PM PT.

While it's unclear if they actually ate anything inside, our guess is they might've. And, seeing how this place is pretty much all about raw fish -- it's a safe bet sushi was likely ordered.

The reason that's a big deal ... there's been some murmurs of late that MM could, perhaps, have a bun in the oven. Some theorized that might've been why she skipped the coronation -- but the conjecture fired up even more so when photos of her hiking last week surfaced.

Folks noticed she appeared to have something slightly protruding under her shirt, near her stomach ... and that served as enough evidence for some to believe she was expecting.

Of course, that little extra belly pop Meg was showing off in the great outdoors could just as easily have been a fanny pack of some sort -- it really doesn't look like a straight up baby bump, even though a good handful of gawkers online were pretty convinced it might be.

Now that we've seen her leave a sushi joint -- a food typically sworn off by pregnant women due to the risks it poses to a growing fetus -- it feels like we can put that notion to bed.