Heat oil in a deep pan. Once the pan is heated, add onion, garlic, chilies, ginger or galangal, and cook until golden brown.
Add mushroom sauce, soy sauce, lemon grass, brown sugar, and tomatoes. Cook for 2 minutes.
Add Chicken stock and bring to boil. Boil for 2 minutes.
Add vinegar and black pepper.
While the soup is boiling, crack a egg into the liquid and rapidly stir to make fine strings of egg. Continue to boil and add the other 4 eggs. Remove the pan from the heat source and cover.