Latching on to the first answer, I was able to find what looks like a decent recipe for arrachera, which was previously posted on Yahoo answers:
1½ lbs top grade arrachera (flank steak)
1 cup pineapple juice
½ tbsp salt
2 tsp black pepper
2 tsp garlic salt
2 tsp onion salt
2 tsp hot paprika
1...
