To prepare the upo, cut about half an inch off both ends. You may cut the upo into halves or thirds for easier handling. Using a small sharp utility knife, cut off the skin.
Then, cut the skinned upo vertically into halves to expose the center. Using a spoon, scoop out the seeds. Cut the flesh into half-inch cubes.
Heat the cooking oil in a pot.
Saute the onion and tomatoes. Do this over medium heat until the vegetables start to liquefy.
Add the garlic. Saute for another minute.
Turn up the heat. Add the ground pork to the pot. Season with fish sauce and pepper. Cook, stirring, until the pork is no longer pink.
Pour in the broth.
Add the upo cubes.
Taste and add more fish sauce and pepper.
Bring to the boil, lower the heat, cover and simmer for about ten minutes or until the upo cubes are tender.