Marinate the pork slices in soy sauce, calamansi juice, liquid seasoning or Worcestershire sauce, garlic, sugar, ground pepper and MSG for about 2 hours.
Heat some oil in a pan and saute onions until soft and set aside.
In the same pan, add more oil and stir fry the marinated pork until brown. Then add the marinade, soup stock or water and simmer for 45 minutes or until the pork is tender. Add more water is the pork is not yet tender and the liquid dries up.
Adjust the seasoning if needed and add the onions as garnishing then serve hot.