Combine all the ingredients under "steak marinade" except for flank steak in a bowl. Whisk to combine.
Pour marinade onto flank steak, and make sure flank steak is covered in marinade. Marinade for at least 2 hours, but no longer than 12 hours.
Combine all the pico de gallo ingredients in a small mixing bowl. Refrigerate and set aside until ready to use.
Grease and heat grill or grill pan. When grill is hot, place flank steak on the grill (shake off access moisture before placing on grill).
Grill steak for a few minutes on each side, then flip and grill the other side for another few minutes. Cook time varies based on doneness preferences. Use a meat thermometer to determine doneness. See chart in notes for steak temperature at different level of doneness.
When steak is done, remove promptly. Place steak on a plate and wrapped in aluminum foil to rest for 5-10 minutes. Slice steak into thin strips.
Heat tortillas either on the grill, stovetop or in microwave.
Top tortillas with sliced steaks, pico de gallo, queso fresco and cilantro. Serve and enjoy!