Heat 1 tablespoon oil in a wok or large skillet over medium high heat. Add ground pork and brown, stirring to break up the lumps. Cook 8-10 minutes until no longer pink.
Add the sugar and 1 tablespoon fish sauce. Cook for another 2 minutes. Transfer to a bowl and set aside.
Heat the remaining 1 tablespoon oil in the wok. Add the garlic and onion and fry until softened, 8-10 minutes.
To the wok add the tomatoes, chicken stock (or water), tomato paste, remaining 2 tablespoon fish sauce and cooked pork. Simmer, stirring occasionally, for 15 minutes.