Preheat oven to 425°. Cut pork tenderloin in half crosswise. Mix garlic, rosemary, cumin, salt, and pepper and rub mixture all over pork.
Heat oil in a medium ovenproof frying pan over high heat. Add pork and cook, turning as needed, until outside is completely seared, about 3 minutes total.
Put pan in oven and roast pork until done the way you like, about 10 minutes for medium (150° on an instant-read thermometer). Let rest 5 minutes before slicing.