Combine all marinade ingredients in a processor and blend well. Pour over flank steaks in a bowl or sealable plastic bag; place in drip proof container. Chill 4 hr up to overnight.
On a hot grill, sear steak well on both sides. Heat to 120ºF internal for rare, 130ºF for medium or as desired, about 10 min. Conversely, sear flank in hot skillet in well ventilated area, basting with marinade, to same temp as above. Remove from heat and let rest for 5 min. Slice very thin (chop to bite-size pieces if desired, combining with any juices) and serve immediately with warm tortillas, rice and condiments.