1. In a large bowl, whisk together all of the ingredients for the marinade.
2. Place the steak in a large plastic zipper bag. Pour the marinade over the beef, seal the bag and shake to evenly distribute the marinade.
3. Refrigerate for at least 1 hour, or up to 8 hours.
4. Heat a grill or a large grill pan over high heat. Brush with oil to prevent sticking. Cook the steak for 5 to 8 minutes on each side and then transfer the steak to a cutting board and allow to rest for 5 minutes.
5. Warm corn tortillas in a dry pan over medium-high heat for 30 to 60 seconds each side, until softened slightly.
6. Thinly slice the steak and chop into small cubes for smaller bites.
7. Serve the steak on the warm tortillas with onion, guacamole, cotija cheese, cilantro or your choice of toppings.