How to Make It
In a large bowl, mix the olive oil with the tomato paste, Aleppo pepper, garlic and Baharat. Add the lamb cubes and stir to coat evenly. Cover and refrigerate for at least 4 hours or overnight. Bring to room temperature before grilling.
Light a grill. Thread the lamb onto 4 long skewers and season with salt. Grill the lamb, turning, over moderately high heat for about 5 minutes for medium meat.
Meanwhile, in a medium bowl, thoroughly toss the onions with 1 tablespoon of kosher salt. Let stand until the onions are slightly soft, about 5 minutes. Rinse and drain well. In a serving bowl, toss the onions with the parsley and sumac. Serve the lamb kebabs with the onion salad and warm pita bread.
Aleppo pepper is a Turkish crushed chile, which is more robust and slightly fruitier that regular red chile flakes. If you can't find Aleppo pepper, substitute 1/4 teaspoon of paprika and a tiny pinch of cayenne.