In a large bowl combine La Tortilla Factory Barbacoa sauce starter and avocado oil. Mix until throughly incorporated.
Coat flank steak with marinade and refrigerate for 2-12 hours. Once it's ready remove from the marinade and lightly pat dry the flank steak with a paper towel.
Grill on a high heat grill for about 3-4 minutes on each side and until it reaches desired doneness.
Remove from heat and rest for 10 minutes. Slice against the grain and serve with on grilled La Tortilla Factory tortilla. Top with Charred Romaine Slaw & Elote Guacamole and enjoy.