Step 1

Combine garlic, lemon juice, 1/4 cup oil, salt, allspice, cinnamon and pepper in a medium bowl. Place beef in a large sealable plastic bag and pour in the marinade. Refrigerate for at least 2 hours or up to 1 day.

Step 2

Preheat grill to high.

Step 3

Remove the beef from the bag. (Discard the marinade.) Brush onions with the remaining 1 tablespoon oil. Divide the beef among 6 skewers and the onions among the remaining 3 skewers. Grill the onions until charred and tender, 10 to 12 minutes per side. Grill the beef, turning once or twice, until slightly charred but still pink in the middle, about 6 minutes. Serve with Tahini Sauce.