In an exclusive preview of the episode 'Now You Sia, Now You Don't!' - shared by CBR - the star makes iconic duo Scooby and Shaggy a plant-based sandwich.
"Like who wants to be on a stakeout when we could be hanging out with Sia?" Shaggy asks.
"And be vegans," adds Scooby - who then swallows the sandwich whole and calls it 'delicious'.
In the next scene, Sia says: "No stop wait. Duh. Can't start our party without my vegan pie-maker and cotton candy machine." The machine then flings a pie directly into Sia's face, to which she says: "It tastes much better this way."
Last year, it was announced the Chandelier singer had joined the cast of vegan documentary Dominion as one of the celebrity narrators.
Sia joined actors Joaquin Phoenix and Rooney Mara - who were announced as narrators in a PBN exclusive - and co-producer Shaun Monson, who directed acclaimed vegan documentary Earthlings.
The episode guest-starring Sia first premiered on September 5 on Boomerang.
You can watch the trailer here