I found the recipe here and it is definitely one of the best marinades I've tried; I think the lime juice/steak combo would make for great fajitas!
2/3 cup vegetable oil
1/3 c. freshly squeezed lemon juice (I think I might try lime juice next time!)
3 Tbl. soy sauce
3 cloves of garlic, finely minced
1 tsp. dried oregano
1/2 tsp. kosher salt
1/2 tsp. black pepper
8 chicken breasts/pork chops or 1 pork tenderloin or a flank/skirt steak
Combine all ingredients except chicken in a mixing bowl or large airtight plastic bag. Whisk or shake well until the marinade is well mixed. Add the chicken breasts to the bowl or plastic bag so that they are covered by the marinade. Cover and refrigerate up to 10 hours (I would suggest marinating for at least 3 hours).