Arrange pork medallions on a cutting board and cover with a sheet of plastic wrap. Using a mallet or the back of a knife, pound the pork until each medallion is fairly flat, about ¼-inch thick.
Cut each medallion into 1-inch square pieces. In a medium bowl, combine salt, baking soda and water. Place pork pieces in bowl and turn to coat.
Place tapioca flour in a large, resealable plastic bag. Place pork pieces in bag with flour and shake meat around until all pieces are coated with flour.
Heat oil in a large skillet over medium high heat. Place pork pieces in oil and fry for 5 to 10 minutes, or until golden brown. Remove pork and set aside.
In the same skillet over medium high heat, combine green bell pepper, red chile pepper, pineapple, onion and tomato and saute for 5 minutes.
Meanwhile, in a separate small bowl, combine white sugar, salt, corn flour, vinegar, ketchup, plum sauce and water. Mix well and pour plum sauce mixture into skillet with vegetables.
Reduce heat to low and let simmer for 5 to 10 minutes, allowing gravy to thicken. Return pork pieces to skillet, mix all together well and serve.
