Quavo stole the flavor for his modest 2018 hit "Bubble Gum" from a Louisiana rapper who says he actually handed Quay the inspiration in person ...

at least according to a new lawsuit. TMZ Hip Hop obtained docs filed by a man named Lamount London -- who goes by L.Mont -- in which he claims he opened for 2 Chainz and Quavo's group Migos at the Saenger Theatre in New Orleans, LA on February 9, 2016.

Following the concert, L.Mont claims he passed Quavo a CD containing his song, "Bubble Gum" ..

. a bouncy NOLA-style track he says he recorded in 2015, in hopes of working together down the line. L.

Mont says he never heard from Quavo -- but claims he heard his own work when the Atlanta superstar released his debut album "Quavo Huncho" and promoted track #18 "Bubble Gum." Quavo's song has amassed millions of plays over the years, and L.Mont is claiming the lyrics, arrangement, melody .

.. everything but the candy wrapper is a direct bite of his work, he says -- and he's now seeking damages over it.

We reached out to Quavo's team but have yet to hear back..