Heat a heavy soup pot over high heat, add the oil, and heat until hot, about 20 seconds. Add the tomatoes and scallions, and stir-fry until fragrant, about 15 seconds. Add the soy sauce and rice wine or sake, and stir-fry over high heat for 20 seconds. Add the water and salt, and bring to a boil. Reduce the heat to medium-low and cook for 2 minutes, skimming the surface to remove any impurities. Add the snow peas and stir.
Slowly add the cornstarch mixture and bring the liquid to a boil, stirring to prevent lumps from forming. Once slightly thickened, remove from the heat and slowly add the beaten eggs, pouring them in a thin stream around the edge of the pot. Carefully stir once or twice so that the eggs form thin streamers. Taste for seasoning and ladle into serving bowls.