You can make this salad with virtually any kind of seaweed you find in clean waters on any North American shoreline. If you are not in North America, you will need to identify specific seaweeds to your oceans. In the Pacific, avoid the feather boa kelp, Egregia menziesii -- it's just too tough to eat in a salad. You will want to keep your seaweeds cool and moist for the drive home, then wash them in cool running water when you are ready to use them. Blanch if you want. Or eat the little crustaceans that hang onto the seaweed (protein!), whichever.
To make the dressing, whisk all the ingredients together in a small bowl until the sugar dissolves.
Get a large pot of water boiling. Boil the sea beans for 1 minute and then plunge into a bowl of ice water. Boil any seaweed you want to blanch (see post above) for 15 seconds, then plunge into the ice water. Pat the vegetables dry and put into a large bowl with any of the seaweeds you want to eat raw.
Toss the salad with the dressing and chill. You want to eat this salad very cold. When you are ready to serve, mix in the green onions and sprinkle sesame seeds on top.
Notes
You can also buy seaweed. Look for wakame, which is the typical seaweed used in salads. You can find it in many Asian stores. It usually comes dried, and will reconstitute almost like fresh. Virtually every sushi restaurant in America uses the dried stuff, so don't worry. You will need about 2 ounces for this recipe.