I briefly mentioned jellyfish in my post earlier this week on 海 (hǎi/ocean/sea). The Mandarin Chinese word for jellyfish is 海蜇 (hǎi zhé), literally "sea sting", referring to one of their more notorious characteristics. According to Wikipedia, the journey of a jellyfish from the sea to the table is quite an extended one, with processing taking up to 40 days. Happily, the jellyfish on sale in Chinese supermarkets has already undergone this processing. It's worth noting, though, that there are two kinds; one is ready to eat, but the other needs to be soaked in water overnight to remove the salt. I don't think there's any great advantage to the kind that needs to be soaked, so it's worth looking out for the ready-to-eat type.
Jellyfish has no flavour of its own, but it's great at soaking up other flavours and providing interesting texture to a dish. I find the texture is fairly similar to the cartilage in chicken feet, which I quite enjoy crunching on at dim sum outings.
On Chinese menus, jellyfish generally appears as a cold dish, shredded and mixed with a savoury dressing based on soy sauce, vinegar, and sesame oil. Sometimes the dish also includes chicken (雞/jī) and/or cucumber (黃瓜/huáng guā or 青瓜/qīng guā).
The chicken may be listed as hand-torn (手撕/shǒu sī), and the character 絲 (sī/shredded) may also appear in the name somewhere; all of the main ingredients are basically shredded, but sometimes this is left implicit. Other ingredients, such as sesame oil (麻油/má yóu or 香油/xiāng yóu), may or may not be listed specifically. Finally, the character 皮 (pí/skin) may also be appended to 海蜇, perhaps in reference to the thinness of the edible part. Hence, there's quite a lot of variation in the name of this dish; I've seen it variously as 海蜇手撕雞, 海蜇拌雞絲, 青瓜海蜇絲, 海蜇黃瓜, and 香油海蜇皮, among other names, including simply 涼拌海蜇 (liáng bàn hǎi zhé), literally "cold mixed jellyfish", usually translated as "jellyfish salad".
Sunflower's recipe for the dish includes both chicken and cucumber, and spices it up with fresh chillies and chilli oil. Ken Hom's Chinese Recipes has a plainer, simpler recipe, which simply involves dressing 225g jellyfish with 2 tsp soy sauce, 3 Tbsp sesame oil, 2 tsp white rice vinegar, and 2 tsp sugar, marinating for 30 minutes, then scattering over 3 Tbsp toasted sesame seeds. I can personally vouch for Sunflower's recipe, though I prefer it without too much chicken in.