In the show there is a scene where frieren reveals to stark (the warrior of their current party) that eisen (the warrior in the old party) would make hamburg steaks for the party on their birthday, as ‘anyone who puts in a hard days work is a warrior’
So the drawing is frieren making a Hamburg steak, for all the warriors competing.
Eisen used to make giant hamburger steaks as birthday presents. It was a custom from his region to thank warriors who put in their all, and later Frieren continued that tradition