Prepare the winged beans by trimming the ends and then cutting into ½-inch diagonal pieces. Set aside.
In a medium pot, bring the pork, water and salt to a boil. Reduce the heat to medium and cook, covered until the meat is tender, about 45 minutes. Remove the pork from the broth, reserving 1 ½ cup of the broth. Let the pork cool slightly and then cut into 1/2 inch pieces. Set aside.
In a skillet, heat the oil over medium high heat. Add the shallot and tomato, and sauté for 2 minutes. Add the pork and saute until brown, about 2 minutes. Stir in the fish sauce.
Add the winged bean, stir and then add the reserved broth. Bring to a boil, cover and cook for 3 minutes, or until winged bean are crisp tender. Stir in the moringa leaves and cook for a minute. Season to taste with salt.
Serve hot with steamed rice.