The singer-songwriter shared the photo on Instagram Wednesday ... kicking off a post full of memes with one thing that's certainly not a joke -- her black underwear showing off her backside.

Lizzo's tossing a sultry look at the camera ... and, reminding everyone she's been working hard for a couple years to get healthier and reach her ideal weight.

As you can imagine ... the Internet's pretty complimentary -- and, the trolls who used to come after the star have completely clammed up.

We told you that Lizzo surpassed her weight goal back in January ... losing 16% body fat in two years -- and sharing a video all about her transformative journey.

At the time, she said it was time to set new fitness goals ... and, it looks like she's setting and accomplishing them -- with this new pic capturing the continued progress she's making.

Lizzo's weight loss journey became public knowledge in September ... when she shared her weight-release reveal. She said her process had nothing to do with the "South Park" Ozempic special that name-dropped her -- but, many online weren't buying it.