Freeze flank steak for 30 minutes until slightly firm. Remove from the freezer and slice the steak across grain on a bias into 1/4-inch-thick strips. Place the steak in a zip-top bag and pour in the ingredients for the marinade. Seal and toss to evenly distribute. Remove excess air from the bag and marinate in the refrigerator for 30 minutes. Weave meat onto individual skewers and lay flat in shallow container.
Heat a grill or grill pan to medium, and cook the beef skewers 1-2 minutes on each side until grill marks appear. Remove from the grill pan with a pair of tongs and set aside. Repeat with the remaining skewers, making sure to never crowd the pan.
For the dipping sauce, char the jalapeños over a gas flame or under a broiler until blackened on all sides. Place the charred jalapeños in paper bag, seal and let stand 10 minutes, then peel, seed and finely chop the jalapeños. Place the diced jalapeños in a small bowl, and whisk in remaining dipping sauce ingredients. Season with salt and pepper and serve alongside the beef skewers.