Step 1Heat a medium saute pan over high heat. Add the soybean oil just until shimmering, then sear the pork on all sides. Remove and set aside the pork.
Step 2In a medium heavy-bottom pot, combine the pork with the soy sauce, mirin, sake, sugar, ginger, chile and oregano along with 4 cups of water. Bring the contents to a boil, then reduce the heat to a simmer and cook, uncovered, until the pork is fork tender, about 2 hours. Add the water as the liquid reduces to keep the pork just submerged at all times.
Step 3Serve the pork in a bowl with some of the liquid poured over.