In a large Dutch oven or wok, heat oil and sugar over medium-high heat, swirling pot until sugar melts and turns a caramel-amber color.
Place pork belly slices in pot and sear on all sides, about 1 minute per side, using tongs to turn.
Pour enough cold water into vessel to cover the pork. Add soy sauce, five spice powder, ginger, garlic, and salt. Bring to a boil and skim any scum that rises to the surface. Reduce heat to low and simmer, uncovered, for 3-4 hours, until pork is very tender and fat is easily penetrated with a spoon. Add water as necessary to keep pork fully submerged.
Remove pork belly and set aside. Strain solids from braising liquid and return liquid to pan. Over high heat, reduce until lightly thickened and glossy. Adjust seasoning if necessary.
Slice pork into 1/3-inch thick slices. Lightly coat in reduced braising sauce.