Mix all the meat ingredients and 1/2 tbsp sumac in a bowl and refrigerate for at least an hour
Soak the wooden sticks if used. You would need 12 to 15 long skewers or around 20 short skewers
In small bowl, mix all the ingredients for the garlic yogurt, refrigerate till ready to serve
Prepare the red onion and parsley garnish: this is the key flavor driver. Sprinkle the salt over the finely sliced red onion. With your hands, squeeze the onions so the salt can really be well mixed. Add the chopped parsley. Drizzle with 1 tablespoon of olive oil, set aside.
Display all the garnish on a platter for guests to help themselves.
Skewers the meat and form a flat elongated shape.
Heat the grill to high, oil the grates well. Grill the meat skewers for 4 minutes on one side, flip them over, and grill the other side for another 4 minutes (you can also use a cast iron grill). Warm up the flatbread or pita bread on the grill. Sprinkle remaining 1/2 tbsp Sumac over the meat before serving.
Serve hot with the garnishes and garlic yogurt sauce. Remove the meat from the skewer, wrap it with the garnishes and yogurt sauce in flatbread or pita bread, and enjoy!