In a large pot, heat the vegetable oil over medium heat. Add the sugar and cook, stirring constantly, until it melts and turns a deep amber color, about 3-5 minutes. Be careful not to burn it.
Add the pork belly cubes to the pot and stir to coat them in the caramelized sugar. Cook for about 5 minutes, allowing the pork to brown slightly.
Pour in the soy sauce, dark soy sauce, and water. Stir in the ginger, garlic, green onions, star anise, and rice wine. Bring the mixture to a boil.
Reduce the heat to low, cover the pot, and let it simmer for about 1.5 to 2 hours, or until the pork is tender. Stir occasionally and add a little water if the sauce gets too thick.
Once the pork is tender, remove the lid and increase the heat to medium-high. Let the sauce reduce for about 10-15 minutes, stirring occasionally, until it thickens to your desired consistency. Season with salt to taste.
Serve hot over steamed rice, garnished with additional green onions if desired.