Preheat the oven to 350 degrees. Pat the tenderloins dry and season with salt and pepper. Heat a large skillet over medium-high heat. Add the oil to the pan. When the oil shimmers, add the pork to the pan. Sear all sides of the pork until golden brown. Remove the pork from the pan and add the plums cut side down. Add the peppercorns, anise, ginger, and zest to the pan, then the wine. Stir in the soy sauce, stock, orange juice, and brown sugar. Arrange the plums in the middle of the pan and place the pork on top of them. Cook the pork in the oven for 15-20 minutes or until it reaches 130 degrees.