According the the Talmud, what can a vegetarian substitute for the traditional shankbone on the Seder plate?

The lamb won't miss it!

a roasted mushroom or beet

just a JFYI, why are yu allowed to use a roasted beet? The reason is because the shank bone is in remembrance of the lamb offering used in the time of the temple. Most families now a days will not use lamb and use chicken instead because we don't want people to mistakenly think that we are offering a passover sacrafice nowadays. The beet or mushroom has to be roasted in memory of the roasting of the lamb, but it doesn't have to be meat at all cuz your not eating the meat, your remembering the meat.

Cool info Yafa!!