Cook the noodles according to packet instruction, drain and keep warm.
Heat the vegetable stock in a saucepan, add the beans and cook for 3 minutes.
Add the wakame, cook for another 3 minutes or so. Turn off the heat.
Meanwhile, mix the miso, soy sauce and mirin or rice vinegar in a small bowl with a spoonful of the soup and make a smooth paste.
Turn off the heat. Add the chopped spring onion pieces and the miso mixture to the soup.
Add the noodles. Reheat if necessary.
Serve warm with sesame seeds scattered on top.