Trim any fat from meat. Using a sharp knife, make a lengthwise cut down the center of roast, making sure not to cut all the way to the other side of the roast. Spread the meat flat.
Place tenderloin between 2 sheets of plastic wrap and pound meat lightly with the flat side of a meat mallet to the shape of a rectangle.
Spoon the salsa evenly over pork. Roll up the tenderloin up jelly-roll style, beginning at the narrow end. Tie the meat with string, first at the center, then at 1-inch intervals all the way to the ends.
Place the meat on rack in a shallow roasting pan. Sprinkle the loin with salt and pepper to taste.
Roast, uncovered, at 375° F for 50 to 60 minutes or until the meat is tender and slightly pink (160 degrees F) and juices run clear.
Transfer the meat to a platter. Wait 10-15 minutes before cutting into equal slices.