Peel and discard the outer, fibrous skin layers of banana heart until you reach the lighter, softer core. Trim off stem and discard. Cut banana core into half and slice thinly. In a bowl of cold salted water, place shredded banana and soak for about 15 to 20 minutes. Using hands, squeeze to release bitter sap. Rinse with cold water and drain well, discarding liquid.
In pan over medium heat, heat oil. Add onions and garlic and cook until limp and aromatic. Add pork and cook, stirring occasionally, until lightly browned. Add chili. Add fish sauce and continue to cook for about 1 minute.
Add banana. Season with salt and pepper to taste. Continue to cook, stirring occasionally, for about 5 minutes or until softened and releases liquid. Add water. Continue to cook for about 10 to 15 minutes or until tender.
Add vinegar and bring to a boil, uncovered and without stirring, for about 3 to 5 minutes. Stir to combine and continue to cook for another 8 to 10 minutes or until liquid is reduced and pork and vegetable are cooked. Serve hot.