In a wide, heavy-bottomed pan over medium-high heat, heat oil until very hot but not smoking.
Add pork in a single layer and cook for about 2 to 3 minutes or until lightly browned. Turn and cook for another 1 to 2 minutes or until all sides are lightly browned.
Add onions and garlic and cook, stirring frequently, until softened.
Add pineapple juice and vinegar. Allow to boil, uncovered and without stirring, for about 2 to 4 minutes.
Add soy sauce, water, peppercorns, and bay leaves. Stir to distribute and bring to a boil, skimming scum that floats on top.
Lower heat, cover and simmer for about 1 1/2 to 2 hours or until pork is very tender and liquid is reduced.
Add brown sugar and stir until dissolved. Season with salt and pepper to taste.
Add pineapple chunks and stir to combine. Serve hot.