For Pork: Preheat the oven to 425 degrees F. Place the black beans in a small bowl and mash them with a fork. Stir in the hoisin sauce, soy sauce, sherry, sugar, garlic, and five-spice powder. Rub about 1/4 cup of the marinade over the pork and place the pork on a rack over a roasting pan. Pour 1/2 cup of water into the pan.
Roast for 15 minutes, then lower the oven temperature to 350 degrees F and continue roasting until the internal temperature reaches 155 degrees F, spooning additional marinade over the pork every 15 minutes or so.
Remove the pork from the oven. Let it rest for 15 minutes before slicing and serving with white rice.
For Rice:Place the rice in a fine-mesh strainer and rinse thoroughly with cold water.
Transfer the rice to a large saucepan and add the water and salt, stirring to dissolve. Stir in the oil and bring to a boil. Let the rice boil for 4 minutes, then lower the heat to a bare simmer, cover the pot, and simmer until the water has been absorbed, 10 - 12 minutes.
Remove the pot from the heat and let stand, covered, for 10 minutes. Fluff with a fork before serving.