Add the olive oil and sear pork until golden on all sides, about 10 minutes.
Lower heat to 250ºF and add orange juice, wine and brown sugar.
Cook with the lid on for 25 minutes or more (until it reaches an internal temperature of at least 145ºF).
Remove the tenderloin and let the sauce thicken. You can add one tbsp. of cornstarch dissolved in a bit of cold water to the sauce while it simmers, to make it creamier and help thicken it. (about 1 minute)
Serve the pork with the white wine sauce and fresh oregano.