Lay The Flank Steak In A Large Non-Reactive Bowl Or Baking Dish. Combine Marinade Ingredients And Pour The Marinade Over The Steak. Make Sure Each Piece Is Well Coated. Cover In Plastic Wrap And Refrigerate For 1-4 Hours. Preheat Your Grill Over Medium-High Flame (You Can Also Use A Cast Iron Grill Pan On High Heat For Stove-Top Cooking). Brush The Grates With A Little Oil To Prevent The Meat From Sticking. Remove The Steak From The Marinade. If You Are Cooking Indoors, You May Want To Brush Off Excess Marinade As The Bits May Burn And Smoke On The Hot Pan. Season Both Sides Of The Steak Pieces With Salt And Pepper. Grill The Pieces For A Few Minutes Only, On Each Side, Depending On How Thin They Are, Until Medium Rare To Well Done, To Your Preference. You May Need To Work In Batches. Remove The Steak Pieces To A Cutting Board And Let Rest For 5 Minutes. Thinly Slice The Steak Across The Grain On A Diagonal. (Optional) Serve With Warm Tortillas (Flour Or Corn). Warm The Tortillas For 30 Seconds On Each Side In A Dry Skillet Or On The Grill, Until Toasty And Pliable. Alternatively, You Can Warm Tortillas In A Microwave: Heating Just One Or Two At A Time, Place Tortillas On A Paper Towel And Microwave Them For 15 To 20 Seconds Each On High. (Optional) Serve With Pico De Gallo (Fresh Tomato Salsa) And Chopped Avocados.