Heat the vegetable oil in a heavy-bottomed pot over medium heat. Add the chopped onion, sliced ginger, and minced garlic and cook, stirring occasionally, until the onion becomes soft and translucent.
Increase the heat slightly and add the beef ribs. Brown the meat on all sides to develop flavor, stirring to ensure even searing.
Stir in the tomato paste until it coats the meat, then add the tomato sauce and mix thoroughly so the ingredients are well combined.
Pour in 1.5 liters (6 cups) of water. Add ground black pepper, sugar, and salt. Bring the pot to a boil, then maintain a simmer and cook for 20 minutes to start developing the broth.
After the initial 20 minutes, add the corn pieces. Continue to simmer over medium heat and cook slowly for 2 to 3 hours, or until the beef becomes very tender.
If the liquid has reduced by about half during the long simmer, add an additional 1/2 liter of water. Then add the squash, plantain pieces, cubed potatoes, and Chinese chorizo. If you want heat, include the green chilies now. Simmer another 15 minutes until the vegetables are just cooked through.
Add the green beans and cook for about 2 minutes so they remain crisp-tender.
Remove the pot from the heat and nestle the pechay on top. Let the residual heat wilt the leaves for a couple of minutes.
Serve the beef pochero hot in bowls or a large communal dish alongside steamed white rice.