There are actually several different kinds, but apparently, the best is made from lamb.
Here’s one Jew’s review:
OK just made 1 batch in the frying pan. It looked a little too lamb-like at first but by the time it was ready it was definitely bacon! Pretty salty, but I think that’s how it’s supposed to be. I have never eaten the real thing but have seen and smelled it many times and this was what I imagined it would taste like
Kosher bacon – your baconest dream come true.
UPDATE: High Praise! to Former Hostage for the Kosher Bacon symbol in the comments: