Cut the tofu into 2cm cubes.
Heat the vegetable oil in a wok and fry the cubes until light brown on all sides. Add the soy, vinegar, honey, sesame seeds & oil, then stir-fry until sticky and golden. Transfer them to a plate.
In a saucepan heat the stock. Cut the pack choi in half (vertically) and cook in the stock for 3 minutes. Take a ladleful of the stock into a small bowl and mix it with the miso paste until smooth. Pour this into the soup.
Finely chop the spring onion, add to the soup. Add the tofu pieces too, then bring to a simmer and serve immediately.