'You Yu Geng' (that's the mandarin pronunciation - I won't even try to phoneticize the Taiwanese pronunciation), is basically julienned squid wrapped in a fish paste, and it's the star in the traditional slightly sweet & sour soup called 'Geng,' loaded with assorted veggies like sliced shiitake mushrooms, bamboo shoots, carrots, wood ear fungus, seasoned with black vinegar, and then thickened with a cornstarch slurry. There's another iteration using pork instead of squid ('Rou Geng'), which can be substituted for the squid version in this recipe. If you don't have a Chinese market in your neck of the woods that stocks this ingredient, then I can't help you. I know you can make fish paste from scratch, but I'm not one who does. So there.
*Bonito shavings (I didn't add this to the recipe this time, but it's a traditional flavoring that my mom uses)