Rinse pork; trim and discard any fat. Place meat between sheets of plastic wrap. With a flat mallet, pound until meat is an even 1/4 inch thick.
In a small bowl, mix paprika, vinegar, garlic, cumin, oregano, and 1/2 teaspoon salt. Uncover meat and rub seasoning mixture evenly over both sides.
Add enough oil to a 10- to 12-inch frying pan over high heat to coat pan bottom when swirled. When pan is hot, add meat and cook until edges turn white, about 2 minutes. Turn meat and brown other side, about 2 minutes. Continue to turn for even color until pork is no longer pink in the center (cut to test), about 8 minutes total. Cut into serving pieces. Add salt and lime juice to taste.
We have loved this recipe since it first appeared in Sunset. I have been serving it for 10 years now. It is a favorite and a classic. I grill it versus the skillet. You need to pay attention as it cooks quick. It can be prepared early and cooked when needed. Just fantastic! It will become a regular in your cooking rotation - the first few years we made it all the time. Can I give it more STARS - deserves 10! For grilling I add the oil and lime juice to the spices and brush it on the pork. I find that cutting the tenderloin in to three sections makes the pounding simpler.