Kebabs
In a small bowl, combine the cumin, coriander, smoked paprika, cinnamon, allspice, salt and pepper.
Place the beef in a large bowl and sprinkle the spice mixture over the top. Toss to coat the cubes of beef.
Thread beef tightly onto four or five 12-inch metal or wooden skewers (soaked in water for 1 hour). Brush the kebabs all over with the olive oil.
Prepare a charcoal or gas grille for medium-high heat, or place a large, heavy griddle pan over medium-high heat.
Grill beef skewers until well browned and instant-read thermometer inserted into center of meat registers 125°F degrees for medium-rare, 8 to 10 minutes, turning every 2 to 3 minutes.
Transfer beef skewers to serving platter, loosely tent with foil, and let rest 10 minutes.
Meanwhile, prepare the sauce.
Serve kebabs, yogurt sauce and pickled onions with pita bread, rice pilaf or couscous, as desired.
Pickled Onions
Combine the vinegar, water, sugar and salt in small saucepan over medium heat. Cook for 3 to 4 minutes, whisking, until sugar and salt dissolve. Place red onion a medium bowl and pour the hot vinegar liquid over the top; toss to coat. Let stand at room temperature 1 hour. Cover and refrigerate until ready to use. Drain before using.
Sauce
In a medium bowl, combine all the Sauce ingredients. Whisk until smooth, adding a tablespoon or two more water, if it is too thick.
