Boil a pot of water to cook the noodles according to the package instructions. Drain and transfer to a large soup bowl. Toss with a few drops of oil to keep the noodles from sticking to each other.
At the same time, heat 2 tablespoons of vegetable oil in wok or pot over medium heat. Add the garlic and the scallion whites, and cook for 30 seconds. Then add the tomatoes and stir-fry for a couple minutes, until the oil starts to turn red and the tomatoes soften.
Add the stock, soy sauce, white pepper, sesame oil, and salt to taste. Cover and simmer for 3 minutes, still using medium heat. Now is a good time to beat the egg in a small bowl and have it ready.
Uncover the wok/pot, turn up the heat slightly, and slowly stir in the beaten egg. Turn off the heat and pour the soup onto the cooked noodles. Top with the chopped scallion greens (you can also add chopped cilantro if you want).