I like to imagine that whomever created Sour Patch Kids candies first tasted sumac! This lip-smacking, tart, sour berry is dried, ground and then savored throughout the Middle East on everything from salads to spice blends to this most famous of the Levant's grilled meat preparations. Sumac is available at gourmet supermarkets and online stores, but if you can't get your hands on it then use more lemon juice and zest.
Marinate the steak: In a small bowl, whisk together all of the marinade ingredients (except the steak of course!). Slip the steak into a plastic food storage bag, and pour the marinade over it. Close the bag and then massage the marinade all over the flank steak. Allow to sit at room temperature on your counter (no longer than 2 hours) while you prep the remaining ingredients. (You can also marinate it overnight).2.
Make the Garlicky Tahini Sauce: In a blender, whizz up all of the sauce ingredients, adding more hot water if the sauce is too thick for your liking. Pour into a pretty bowl and set aside. (If you're making this the night before, store it in the fridge. The next day, let it come to room temperature and if it's too thick, thin it out with a little more hot water. Make sure you taste it again and adjust for salt and lemon juice.)3.
Make the Beet Tabbouleh: In a large bowl, add the beets, parsley and mint. In a small bowl, whisk the lemon juice and extra-virgin olive together, then pour the mixture over the salad. Season with the salt and pepper. Stir together with a fork. Just before serving, stir in the cucumber (so that the cucumbers don't turn pink!).4.
Cook the flank steak: Heat a cast iron griddle over medium heat until evenly hot. Using tongs, place the flank steak on the griddle (it should sizzle happily!), and cook on the first side for 5 minutes. Carefully flip and then cook for 3 to 5 minutes until a meat thermometer inserted into the thickest part of the steak registers 140°. Remove to a plate, cover loosely with foil and allow the meat to rest for 5 minutes. (You can use this time to warm up your pita bread)5.
To serve, slice the meat very thinly against the grain. Pour any accumulated juices over the sliced meat to keep it moist. To build the sandwiches, pile the meat on a piece of warm pita. Spoon the creamy tahini over the top then finish with a couple of spoonfuls of the beet tabbouleh. Either roll up or fold over the pita, then dive into a taste of Middle Eastern sunshine!