Assemble all wet and dry ingredients in a bowl and whisk together. Pour over flank steak and marinate for a minimum of an hour. (Can be held overnight.) Remove flank steak from refrigerator and allow to come to room temperature when you start the outdoor grill, about 15 to 20 minutes prior to grilling. Grill flank steak until internal temperature reaches 140°F. Allow to rest for about 5 minutes and slice very thin against the grain. Reserve some of the cooking juices and drizzle back over cut flank steak.
Prepare fresh pomegranate arils, if necessary.* Slice cucumbers very thin, preferably on a mandolin, and place in a bowl. Assemble remaining ingredients in a bowl and toss with cucumbers. Allow to sit for 45 minutes. (Can be prepared a day in advance to really enhance flavors.)
Grill tortillas until warm and crisp. Place a layer of thinly sliced flank steak on each tortilla. Add Pomegranate-Cucumber Kimchee on top and drizzle a small amount of Sriracha. Garnish with a sprig of cilantro and lime wedge.
* To prepare fresh arils, score 1 large POM Wonderful Pomegranate and place in a bowl of water. Break open the pomegranate under water to free the arils (seed sacs). The arils will sink to the bottom of the bowl and the membrane will float to the top. Sieve and put the arils in a separate bowl. Reserve 1/4 cup of the arils from fruit and set aside. (Refrigerate or freeze remaining arils for another use.)