Heat a large pan, then add the oil. Add the garlic and scallions and cook over medium heat, stirring for 3 minutes, until slightly softened. Add the bell pepper and cook for an additional 5 minutes, stirring.
In a bowl, mix the cornstarch with enough of the stock to make a smooth paste and stir it into the pan. Cook, stirring, for 2 minutes. Stir in the remaining stock, the soy sauce, and rice wine, then add the pork, lemongrass, chile and ginger. Season to taste with salt and pepper. Bring to a boil, then reduce the heat and simmer for 25 minutes.
Cook the noodles according to the package directions. Remove from the heat, drain, then add to the soup along with the water chestnuts. Cook the soup for an additional 2 minutes, then remove from the heat. Ladle into warmed bowls, and serve immediately.