Season steak on both sides with salt and pepper.

In a mixing bowl, stir together the marinade ingredients.

Place flank steak in a bowl or large ziplock bag and pour marinade over steak.

Seal/cover and refrigerate, allowing the steak to marinade for 2 - 5 hours. Remove steak from the refrigerator 20 minutes before grilling.

Heat grill to high and brush the grill grates lightly with oil. Lift steak from the bag of marinade, allowing excess marinade to drip off.

Place steak on the grill and cook for about 3-5 minutes per side, or until desired doneness (depending on whether you like yours medium rare or well done).

Transfer steak to a cutting board, cover with aluminum foil and allow to rest 5 minutes. Cut the steak, against the grain, into very, very thin strips.

Warm corn tortillas on a hot dry skillet. Top with steak, pico de gallo, sliced avocado and hot sauce, if desired. Serve with a side of Mexican rice if you'd like.