Preheat your oven to 450 degrees. Place a cast iron skillet or dutch oven over medium heat (make sure its oven safe).
Trim the fat/connective tissue from your pork, if it has any. Salt the outside of the pork (should be about 1-2 teaspoons). Combine all other spices/herbs and rub on the pork.
Add oil to pan, and then pork. Brown for 4-5 minutes on the first side. Flip pork and roast in the oven until cooked to your desired doneness (I'm a medium dude, so I pull at 145-150 deg F), 15-20 minutes.
Let rest for 3-4 minutes, then slice and serve along with that chimichurri sauce.