Bruise the stalks of lemongrass with a mallet and cut into three sections. Peel and slice the galangal into very thin slices. Add the lemongrass and galangal to a pot with the 2 cups of water. Bring the water to a boil, then simmer and cover the pot for about 7-10 minutes. Remove the galangal slices.
Remove the lid and increase the heat so the water is between a simmer and boil. Add in the chicken cubes and ¼ tsp. of salt. After cooking for a minute, add in the daikon radish, fish sauce, coconut palm sugar and coconut milk.
Allow the soup to just simmer and not go above that point or else you will risk curdling the coconut milk. Stir occasionally and allow the chicken and daikon to cook for about 5-7 minutes.
Add in the soy sauce, chopped red onion and steamed sweet potato cubes. If you’d like to add mushrooms, you can add small pieces of oyster mushrooms or chopped creminis now. Remove the lemongrass slices from the soup.