Kesha -- Served With Dr. Luke Lawsuit ... With a Fancy Chicken Assist

Kesha got served Monday by her producer Dr. Luke -- whose legal team enlisted the help of one of the most clever process servers of all time ... or maybe just the hungriest.

The process server showed up at Kesha's L.A. home and slapped legal docs -- connected to her nasty legal battle with Luke -- on the front door. Here's the clever part ... the stickers holding up the papers are from a Rainbow Acres roasted organic chicken package.

The process server's ingenuity might have gone unnoticed by most -- but we know food, and immediately recognized the sticker.

As for whether this counts as effective service of Luke's lawsuit -- probably not, under California law. But if nothing else ... the stickers gave some TMZ staffers a great idea for lunch.

Yes, it was delicious.