I am not Yemenite and bought frozen Jachnun. The package says to cook for 8 hours. Most recipes online talk about cooking it overnight.
My question is then - isn't turning raw dough into cooked dough considered cooking on shabbat??
While you may not start or enhance the cooking process on Shabbat, you are allowed to leave a dish to cook if the cooking process started before Shabbat began.
You would put the food into a low oven or slow-cooker before the start of Shabbat and take it out the next day when you want to eat it. You may not interfere with the food until you take it out and you may neither adjust nor turn off the oven until Shabbat ends.
There are some other considerations, such as how cooked does the food have to be when Shabbat starts, but my main point is that you start the food cooking while you are still allowed and leave it to cook through on its own.