Prepare all the ingredients.
Marinate the fish evenly on both sides with 1/4 tbsp of salt. Set it aside.
Place a pot on the stove over medium-low heat.
Add all the herbs to toast - shallots, bird's eye chillies, galangal, garlic, lemongrass, cilantro roots, kaffir lime leaves. Toast them for about 3 minutes, or until super fragrant and lightly charred. Make sure to stir often to toast them all evenly.
Pour in the chicken stock, or water. Stir lightly before adding the tomato wedges, and the seasonings: salt, sugar and fish sauce. Give it all a stir to evenly distribute the seasonings. Cover the pot and let it come to a rolling boil, for about 2 minutes.
Open the lid, and gently add the marinated fish. Do not stir the soup once the fish is added. Then, wash and add the oyster and shimeji mushrooms. Add the cherry tomatoes. Close the lid, and let them boil vigorously for another 2 minutes, or until the fish is fully cooked.
Open the lid, and gently stir the soup. It should be very fragrant by now. Taste and adjust as preferred. Switch off the heat.
Add the chopped spring onions, parsley, and basil leaves. Gently submerge them into the soup, stirring lightly.
Break the fried chillies and sprinkle them all around the soup. Pour the lime juice. Stir gently to mix it all together.
Serve with some white rice, or on its own!