Preheat your oven to 450°F. Line a roasting pan with foil. Fit it with a rack and lightly grease the rack.
In a small bowl, use a fork to mix the kosher salt, black pepper, garlic powder, oregano, cumin, thyme, and smoked paprika.
Sprinkle the seasoning mixture all over the pork, then use your hands to rub it in, making sure it adheres.
Heat a large skillet over medium-high heat for about 2 minutes. Add the avocado oil and swirl to coat. Gently place the pork in the hot skillet. Sear for 2 minutes on the first side, without moving, to form a well-browned crust.
Use tongs or two wide spatulas to gently flip the pork to the other side, and sear it for 2 minutes on that side. Finish by searing the two remaining sides, 1 minute each.
Turn the heat off. Use tongs to transfer the tenderloin to the prepared roasting rack. Place it in the hot oven and roast until an instant-read thermometer registers 145°F (medium), 20-30 minutes. If roasting for longer than 20 minutes, cover the pork loosely with foil to prevent the top from burning.
Remove the tenderloin from the oven. Loosely cover it with foil and allow it to rest for 10-15 minutes before slicing and serving.
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Notes
If using any salt other than Diamond Crystal Kosher Salt, including Morton kosher salt, use half the amount listed.
As an alternative to searing in a skillet and then roasting in a pan on a rack, you can sear the tenderloin in an ovenproof skillet and then transfer the skillet to the oven for roasting.
In 2011, the USDA lowered its temperature recommendation for cooking whole cuts of pork from 160°F to 145°F with a 3-minute rest period. This means the pork may still look slightly pink when it reaches 145°F.
Searing the tenderloin before baking seals in the juices and enhances its flavor. However, I have experimented over the years and found that simply baking it until browned and cooked through produces comparable results with less effort. To use this method, mix the spices with two tablespoons of olive oil. Dry the tenderloin and coat it with the mixture. Place it on a rack fitted into a rimmed baking sheet. Bake it in a 425°F oven until it reaches 145°F, about 30 minutes for a 1.25-pound tenderloin.
You can keep the leftovers in an airtight container in the fridge for 3-4 days. They can dry out when reheated, so reheat them gently, covered, in the microwave at 50% power. You can also freeze the leftovers for up to three months and thaw them overnight in the fridge before reheating.