Rav Hisda teaches that if someone cooks food on Shabbat by using the heat from the hot-springs in Tiberias, he is not held liable for cooking on Shabbat (one of the 39 prohibited activities on Shabbat), but he would be held liable for cooking the Passover sacrifice, which, as we learned, is forbidden, were he to do it in the hot-springs. Rava explains that the hot-springs in Tiberias are not considered “fire” with regard to the rules and regulations of Shabbat, so no formal cooking takes place. On Passover, although it would not be considered cooking, neither is it considered broiling, which is what one must do in order to fulfill the mitzva of tzli esh (Shmot 12:8-9).
The Me’iri points out that there are variant readings in the Gemara as to whether the source that is quoted is
Pasuk 8 – And they shall eat the meat that night, roasted by fire…
Pasuk 9 – It should not be eaten raw, nor boiled in, rather roasted by fire…
The difference between the sources is whether the method under discussion is considered negation of a positive commandment (8) or transgression of a negative one (9).
The very suggestion that the Pesah might be cooked in the hot-springs of Tiberias is a strange one. The Passover sacrifice, which is considered kodashim (consecration), can only be eaten within the precincts of Jerusalem, and if removed is considered defiled and cannot be eaten! It is unlikely that the Gemara is discussing a situation where water from the hot-springs was imported to Jerusalem, as it would have cooled down so much that it could not have cooked anything.
Although the simple explanation is to say that the Gemara is using the hot-springs of Tiberias as an example of non-fire-related cooking methods, which would apply, for example, to cooking in water heated by the sun – or, perhaps, by microwaves – (this appears to be the approach to the Mishna suggested by Maimonides), Rav Shlomo ha-Kohen suggests that the reference might be to a historical period before the Temple was built, when the sacrifice could be brought anywhere in Israel.