For the marinade, blend all of the ingredients in the blender until smooth. Leave 1/4 cup aside.
Marinate the flat iron steak for 5 hours in a zip lock bag.
Cook the steak on the grill for 4 minutes on each side until medium rare. Allow to rest for 5 minutes, then slice.
Warm the tortillas up on the grill for about 10 seconds on each side.
Layer the tortillas with iceberg lettuce, pico de gallo, avocado, queso fresco cheese, and corn.
Place the sliced steak on top and drizzle with Cholula Original and serve with the reserved marinade.