Trim off stem of banana heart. Peel and discard the outer, fibrous skin layers of banana heart, until you reach the lighter, softer core. Cut in half and slice thinly. Soak in cold water for 20 minutes then squeeze to release bitter sap. Rinse and drain well. Set aside.
In a pan or wok, heat cooking oil.
Saute garlic then add onion and cook until translucent.
Add pork and cook, stirring occasionally until color turns light brown.
Add fish sauce and continue to cook for about 5 minutes or until pork is tender.
Add the banana heart. Stir occasionally and cook until softened and releases liquid, about 5 minutes.
Add water, cover and simmer for 5 minutes.
Add vinegar. Cook uncovered without stirring for 5 minutes.
Add chili pepper (if desired). Stir and continue to cook for another 10 minutes.