Soak the arame in water for 20 minutes. Drain, then place the arame in a medium skillet with the apple cider. Simmer, uncovered, until the cider has completely evaporated, about 10 minutes. Transfer the arame to a bowl and let it sit for a few minutes to cool.
Add the cucumber, lemon juice, spring onions, onions, jalapeno, coriander and garlic. Mix thoroughly to combine and season with salt to taste.