Using a medium bowl, combine the canola oil, soy sauce, vinegar, lemon or lime juice, Worcestershire sauce, mustard, garlic, and ground black pepper. Place meat in a large zip loc baggie and pour marinade over the steak. Turning meat to coat thoroughly. Refrigerate for at least 2-3 hours or overnight.
Cook steaks until they reach a desired doneness. I did mine in a skillet.
Slice meat thinly going across the grain. I actually didn't have to do this since our commissary sells flank steak sliced for fajitas.
While meat is grilling, saute onions and peppers in olive oil and salt until tender.
Serve with meat on a tortilla. Add sour cream, guacamole and or salsa. We used sour cream, cheese, and salsa. You could add lettuce too if that's something you like!