Season the tomatoes and shitake mushroom with salt and allow them to sit for a couple of minutes before using.
Heat the oil in a saucepan. Add the garlic and onion (please do not overcook) tomatoes and mushroom and cook, stirring, for 2 minutes or until the tomatoes start to soften.
Add the chicken stock or water. Bring to a simmer.
Then stir the soup to form a vortex in the center. Pour the egg into the center of the vortex and stir vigorously to form the lacy egg.
Add the cornstarch mixture, salt, and pepper. Simmer for another minute to thicken. Add the spring onion before serving