Put 2 litres water into a large saucepan, add the salt and bring to the boil. Add the soba noodles and cook for 4-5 minutes, uncovered, or follow the packet instructions. Drain, refresh under cold water, then drain well again. Cover and refrigerate.
Put the stock, wine, ginger and onion in a large saucepan. Bring to the boil, then add the chicken and simmer for 6 minutes. Turn off the head and cover with a lid, allowing the chicken to cool in the stock - it will continue to cook during this time. Remove the chicken from the stock. Use your hands or a fork to shred the meat. Discard the stock.
Combine all the dressing ingredients and mix well. Combine the chicken and noodles in a bowl, add sufficient dressing to moisten and gently mix. To serve, pile the noodle mixture into a large bowl and sprinkle with sesame seeds. Serve with any remaining dressing.