Soak hiziki in a large pan of filtered water, then transfer to a fresh pan and soak again. Transfer to a colander and rinse. In a pot, heat the oil and sauté the onions on low heat. Stir in mustard. Dissolve the salt into the water. Add the hiziki to the cooked onions. Then add the salt water solution and bring up the heat. Reduce to simmer and cover. Check back in 10 minutes.
Fold washed and small diced cabbage into the above mixture and continue to simmer. After liquid has cooked down, fold in peppers, remove from heat and let cool. Store, cover and refrigerate. Shelf life of 3 days.
Source: James Thomas of R. Thomas Deluxe Grill in Atlanta