Mix pork, shrimp, egg, fish sauce, water, sugar, both oils, pepper, cornstarch garlic and scallion. Form into 12 meatballs. Saute meatballs until well browned on all sides. Meanwhile combine tomatoes, water, fish sauce, ketchup, sugar and cornstarch. Simmer until well thickened about 15-20 minutes. Place meatballs in rolls and lather on the sauce.