Trim about 2 inches from the kangkong stalks and discard. Cut kangkong into 3-inch lengths, separating the sturdier stalks from the leaves. Wash thoroughly and drain well.
In wide skillet over high heat, heat oil. Add onions and garlic and cook, stirring regularly, until limp. Add pork and cook, stirring regularly, until lightly browned.
Add vinegar and bring to a boil. Continue to cook, without stirring, for about 2 to 3 minutes. Add soy sauce and water. Bring to a boil for about 1 to 2 minutes. Lower heat, cover and cook for about 8 to 10 minutes or until pork is tender and sauce is reduced. Season with pepper to taste.
Increase heat to high. Add kangkong stalks and cook, stirring regularly, for about 1 to 2 minutes. Add kangkong leaves and cook, stirring regularly, for another minute or until just wilted and covered with sauce. Remove from heat and garnish with fried garlic bits, if desired. Serve hot.