Make the marinade and dressing: In a bowl mix the tahini, water, olive oil, lemon zest and juice, garlic, cumin, salt and pepper. Stir until well combined. Take 6 tablespoons of the marinade and mix with the yogurt in a separate bowl and mix until creamy. Add the parsley. Set it aside for later. If using wooden skewers soak them in cold water while preparing the pork.
To prepare the pork: Place the pork pieces in a bowl and season with pepper. Pour the remaining marinade over the pork and toss until completely coated. Leave to marinate for 30 minutes if you have time.
Season the pork with salt then put 3 pieces of pork on each skewer, alternating with pieces of onion. Heat the grill or barbecue to high. Cook the pork for 6 minutes on one side then turn and cook for 4 minutes on the other side.
To make the salad: Mix all the ingredients together then season and taste.
To serve: Heat the flat breads. Either let everyone fill the flatbreads themselves or spread some yogurt over each one, top with the lettuce, then the pork and onion which you have taken off the skewers. Follow on with some salad and drizzle over some more dressing. Fold the flat bread over and enjoy!