Place whole tenderloin first on the hottest side of the grill, closing the lid and letting each side sear for about 2 minutes over the direct heat. Leave it alone. After the time has elapsed, turn the meat one quarter-turn, letting the next side sear. Depending on the size of your tenderloin and the shape of the cut, you may do this four times, or fewer. Once the meat has developed a nice brownish char on the outside, you can move it to the cooler part of the grill and let it cook longer at a slightly less severe temperature. On a charcoal grill, move your pork to the side away from the coals, positioning the meat so that it's not in direct heat. On an electric grill, position the meat next to the heated grate. Close the lid to trap the heat in the grill, leaving the top-vent on your grill about half open, if your grill has one. Many grillers get nervous closing the lid, thinking something terrible is going to happen if you can see the meat the whole time. Try to let go of this concern. Grilling over extremely high heat with the grill open is inefficient and uneven, making it easy to dry out the pork and overcook it. Use the grill the way it was meant to be used: close the lid, set a timer, and kick back while the meat cooks. Over the course of the cooking time, you might open the grill once or twice to turn the pork over and make sure it isn't drying out. Keep an eye on the coals to make sure the heat stays up and the temperature in the grill remains relatively constant, but try not to fiddle with it too much. Leave the meat alone and let it cook. After 20 minutes, it should be close to done. If you use a meat thermometer, the internal temperature should be somewhere between 140 to 155 degrees F (68 degrees C). Put your meat on a cutting board, or a platter, and cover with tin foil to let the meat rest before carving it up. It'll be much juicer and more tender if you let it sit for a couple of minutes. Resist the urge to dig in! Meat isn't rested because it's too hot to eat, it's rested to make it more...

TL;DR in Vietnamese:
Nướng sơ thịt lợn thăn khoảng 2 phút một bên. Chuyển thịt sang phía vỉ nướng ít nóng hơn. Nướng khoảng 20 phút. Gắp thịt ra khỏi vỉ nướng và để nguội 15 phút. Cắt thịt thành miếng dày khoảng 2 cm và ăn ngay.