President Joe Biden is in L.A. this week to fundraise for his reelection campaign -- but he's also out here spreading the wealth ... including with some Jacksons for the common folk.

JB and a bunch of politicians and Secret Service agents hit up a Mexican restaurant in the Baldwin Hills neighborhood ... where he popped into CJ's Cafe for lunch, although -- we're told he ended up ordering a breakfast item.

A CJ rep tells us Joe had a hankering for a basic breakfast burrito -- complete with ham, eggs and bacon ... and we're told the Prez even ordered an orange juice to wash it down.

He was there with Mayor Karen Bass, BTW, and CJ's tells us she was also feeling eggs for lunch -- going in on a plate of scrambled eggs with cheese, tomatoes and toast. Yes, they're not necessarily Mexican dishes, per se, but hey ... this is what they were in the mood for.

Anyway, we're told Biden and Bass paid separately ... and that their teams took care of their bills with respective credit cards. However, CJ's says Joe left a little something extra for the crew ... namely, a $20 tip which we're told he paid for with cash.

You can actually see him reaching into the old wallet in this photo here ... and his total bill also appears to be on display as well. It was about $30 -- the cost of grub in this economy!

And yes ... a bunch of people there in the restaurant were eager to snap some pics with Joey -- and he happily obliged, including photos with the managers/owners of the joint.

And no, believe it or not ... we're told CJ's wasn't shut down for this spontaneous pop-in.

POTUS left after eating, and he went on to deliver a speech at a local library. He was hobnobbing around L.A. all morning -- and best believe he had a bunch of cops tailing him just about everywhere he went ... including his own motorcade, complete with a Secret Service detail.

Word is, Joe's gonna jet on up to San Francisco later today ... and his Cali tour should come to an end by Thursday before he heads back to D.C. to get back to the people's business.

Pretty cool seeing him in the City of Angels ... pretty surreal too, if we're being honest. We see a lot of celebs around here -- but when Joe's in town ... the streets tend to shut down!