Heat oven to 250ºF.
Combine kosher salt, black pepper, and cumin in a shallow dish. Roll roast in seasonings, coating well.
Set a cast-iron grill pan over high heat. Once the pan is hot, brush the roast with the olive oil, and sear on all sides, 8 to 10 minutes total cooking time. Remove the roast to a plate, cover with aluminum foil, and allow to rest for 10 to 15 minutes.
Place the roast back onto the grill pan, put in the oven, and cook until it reaches an internal temperature of 135ºF, 15 to 20 minutes. Remove from the oven, wrap in foil, and allow to rest for 30 minutes before slicing and serving.