The sliders appear to be fairly simple: just grilled lean beef and pickles on a King's Hawaiian roll (the current description of the sliders just reads, "Slide into Summer with King’s Hawaiian").
They officially launch on May 13, 2019 but you can get them early, and with free delivery, if you order with UberEats using the code "FATSLIDER" through May 15, 2019.
Photo via Fatburger.