1. Preheat the oven to 350 degrees Fahrenheit.
2. You can combine the black pepper, garlic powder, and salt in a mixing bowl. You should rub it all over the meat.
3. Then get a roasting pan, and place the roast on a rack in the pan. If you don’t have a rack, you can try three celery stalks laid side by side.
4. Proceed to roast for 20-25 minutes per pound until internal temperature reaches 145-160°F. *The USDA considers 145°F to be a safe temperature for pork. The core will be wet and slightly pink. Though you can choose the 160°F temperature if you prefer your pork totally white and thoroughly done.
5. You should allow for 30 minutes of resting time after covering the roasting pan with foil.
6. Heat up the oven to 475 degrees Fahrenheit. Remove the thermometer and uncover the roast. Place the roast in a clean pan and continue to cook for an additional 10 minutes.
7. Carve and serve right away.

You can watch this video recipe to know how to cook a 5ln pork loin, and how long to cook the meat.