Slice flank steak perpendicular to the grain
Combine the marinade ingredients. Pour over flank steak in a Ziploc bag. Marinate in refrigerator for at least 30 minutes.
Heat oil in a pan over medium heat. Fry the marinated steak.
Prepare corn tortillas by brushing with olive oil and heating in a non-stick skillet over medium heat. 45 seconds on each side.
Remove from heat and fill mulitas with flank steak, cheese, and other filling ingredients. Place another heated tortilla on top.
Place tortilla back on skillet and cook until it develops a golden-brown crust. Flip over and cook the other idea.
Remove from heat and serve.