Although this dish is often called Hijiki Salad at Japanese restaurants in the US, I'm guessing this was a deliberate mistranslation. The Japanese name for this dish is Hijiki No Nimono (ひじきの煮物) which literally translates to "simmered hijiki". I suppose "hijiki salad" is a more marketable name, and it's not entirely inaccurate given that this dish is loaded with both land and sea vegetables.
Although Hijiki No Nimono is a cooked dish, it's typically served at room temperature. This is partly because Japanese meals are usually served with many small bowls of sides called kobachi (小鉢 literally "small bowl"). Since it would be pretty tough to prepare 5 sides and keep them all warm, some of them are made ahead so that they can be quickly dished out. The other reason why this Hijiki No Nimono is served at room temperature is that it needs time to rest to taste its best. if you serve this hot out of the pan it's going to taste a little bland, but leave it in the fridge overnight and you'll be treated to a mouthful of earthy, briny, nutty flavors.
While most people think of adding sugar to a dish to make it sweet, in Japanese cuisine, sugar is used as an ingredient to balance salt, which is how Japanese dishes get their mellow taste. I like using unrefined sugar (often labeled evaporated cane juice) for its extra flavor, and by adding it in while sauteing the carrots, the sugar has a chance to caramelize, imbuing the finished Hijiki Salad with the complex flavor of caramel
Lastly, I like adding some aburaagé (fried tofu) to Hijiki No Nimono as a protein because its spongy texture makes it perfect for absorbing all the flavors in this dish, releasing them into your mouth when you bite into a piece. They're like little flavor bombs distributed throughout the hijiki. If you can't find aburaagé in your area, or "spongy" isn't a texture you're into, you can replace this with your favorite protein such as chicken, edamame, or shrimp.
- Add the dry hijiki to a bowl and cover with plenty of water. Let it rehydrate for 20 minutes and then drain and rise.
- Prepare the enoki mushrooms by trimming off the bottom third and discarding and then cutting the remaining enoki into thirds (about 1 1/4-inch long pieces).
- Heat a frying pan over medium-high heat until hot and swirl with oil. Add the julienned carrots, enoki, and sugar and saute until until the mushrooms have released some liquid, and that liquid has evaporated.
- Add the aburaage and continue sauteing for another 30 seconds.
- Add the hijiki and toss to coat evenly with oil, then add the dashi, sake, soy sauce and salt.
- Turn up the heat to high and cook tossing frequently to reduce the liquid and coat the hijiki evenly with sauce. It's done when there is no liquid left in the pan.
- Finish by tossing the hijiki together with the sesame seeds.