Add water in, bring to a boiling and simmer for 10 minutes over slowest fire. Place all the other vegetable in. Cook for another 10 minutes until all the vegetable are soft. In the mean time, slice mushrooms and wet the mushroom slices and coat them with a thin layer of starch.
Place mushroom slices in if you are using. Cook for another 2-3 minutes. Add salt, light soy sauce if you are using and ground pepper. Drizzle sesame oil in and serve hot.