Preheat the oven to 400°F (200°C). Butterfly the tenderloin by halving the thickness so it opens up like a book into a long, flat piece. Set aside.
Combine the brown sugar with the chili powder and cumin. Rub over all sides of the meat. Place the pork on a lightly oiled ovenproof rack set on a foil-lined baking sheet. Roast, turning once, for 15 min. (or until internal temperature reaches160°F/71°C on an instant-read thermometer). Rest for 5 min., slice thinly.
Arrange the shredded romaine on a platter. Top with the sliced pork, corn, red pepper, celery and onion. Drizzle with dressing and serve.
Cumin and chili powder give this meal a kick without the need for salt