Stir together the spice mix ingredients in a small bowl. Divide the dry rub in half and sprinkle one half all over the flank steak and use your fingers to massage the dry rub into the steak. Place the other half in a ziplock bag or bowl with a lid for later.
In a gallon size ziplock bag, add the coconut aminos, orange juice, lime juice, olive oil and garlic then close the lid and shake to combine. Add the steak, zip it shut and roll around in your hands to fully coat. Place the steak in the fridge for at least 4 hours or overnight if possible.
Discard the marinade and pat the steak dry. Sprinkle the other half of the dry rub all over the steak and massage it into the steaks on all sides.
Turn the grill on and preheat to high with the lid closed. (See notes for oven and IP instructions). Add the flank steak to the hot grill then turn the heat down to medium and close the lid. Grill for 15-18 minutes, flipping halfway through until the steak is cooked through to medium rare and reaches an internal temperature of 145°F.
Remove the steak from the heat to a clean plate and allow to rest for 15 minutes.
While the steak is resting, prepare any toppings like guacamole or pice de gallo and warm the tortillas on low in the oven.
Once the steak is rested and cool enough to handle, dice the steak into small pieces.
Add the steak to the warmed tortillas and top with desired toppings.