Make the marinade by mixing together the sugar, salt, soy sauce and cornflour slurry. Mix in the pork, let marinate for 15 minutes.
In a small bowl, mix together the tomato ketchup and water to make the sauce. Set aside.
Heat a large frying pan with 1 tablespoon oil over high heat. Stir-fry the pork until done, about 4-5 minutes. Set aside.
Heat the same large frying pan with 1 tablespoon oil over high heat. Stir-fry the garlic until aromatic, about 2-3 minutes. Add the onion, shallot, salt and soy sauce, cook until soft, about 3-4 minutes. Stir in the tomatoes with sugar, mix well until soft, about 3-4 minutes. Add the sauce, stir, cover and simmer for 2 minutes. Adjust the seasoning accordingly and serve.
Black soy sauce is thicker and richer than ordinary soy sauce. It can be purchased from Chinese/Oriental speciality stores.