Soak the arame for 5-10 minutes in cold water. Cut the nori sheet into small pieces.
Finely chop the red onions and fry them in a frying pan sprinkled with oil for 2-3 minutes. Cut the shiitake into small pieces and cut the chestnut mushrooms into slices. Add and fry until golden brown in 3-5 minutes.
Boil the noodles in a pan with plenty of boiling water for 3-4 minutes. Drain and rinse with cold water.
Mix the sunflower butter, genmai miso and ume paste together in a glass. Fill the glass with water and mix into an even sauce.
Deglaze the onions and mushrooms with a dash of sake. Keep stirring. Turn down the heat a little.
Drain the arame and rinse with cold water. Add the arame and the miso sauce to the mushrooms. Let it boil gently until the sauce has the right consistency. If needed, add another glass of water and let it boil down.
Put the noodles on the plates. Divide the mushroom sauce over it and garnish with the pieces of nori and black sesame seeds.
Not so much of a seaweed fan? Replace the arame for sengiri daikon (dried white radish).