Shawn Mendes Shows Off Lean Physique Hiking Topless in L.A. With Pal

Shawn Mendes is taking a break from his concert tour for a hike in L.A. with a friend ... and the singer is showing no "Mercy," looking leaner than ever!

Shawn's without a shirt here -- unclear if he just gone done doing laundry on his washboard abs -- looking shredded as he's walking barefoot on a trail in L.A.'s Griffith Park after taking off a pair of hiking shoes.

Shawn was all smiles Thursday, showing off his tattoos and a simple gold-chain necklace, chatting it up with his unidentified pal, who opted for slide slippers and a white T-shirt.

Earlier in the day, we spotted Shawn on the street, wearing a yellow tee, flared brown pants and hard black shoes, and this time his buddy's wearing black socks with his sandals, both of them rocking sunglasses.

Shawn's pretty comfortable strutting his stuff on the street ... we saw him doing topless chores in October outside his house -- and judging by this week's pics, he's been working hard to get leaner.

As we've told you, Shawn's been sharing he's been exploring his sexuality, telling concert audiences last fall it's all a work in progress ... after he was linked romantically to Camila Cabello and Sabrina Carpenter.