Often sold by street vendors, this Lebanese favorite is a large lamb kebab that is marinated overnight, threaded onto a long skewer, and placed in front of a vertical grill. The meat rotates and cooks, allowing the shawarma seller to slice it and make sandwiches. Although our lighter homemade version is baked rather than skewered and grilled, the flavor is very close to that of the real thing.
Trim fat from lamb. Combine 2 cups onion and next 6 ingredients (onion through thyme) in a large zip-top plastic bag. Add lamb to bag; seal. Marinate in refrigerator 2 hours, turning occasionally. Remove lamb from bag; discard marinade.
Preheat oven to 350°.
Place lamb on a broiler pan; insert meat thermometer into thickest portion of lamb. Bake at 350° for 1 hour or until thermometer registers 145° (medium-rare) to 160° (medium). Let stand 15 minutes. Slice lengthwise into thin strips.
Spread each pita with about 2 1/2 tablespoons Yogurt-Tahini Dip. Divide lamb, red onion, mint, tomato, and pickles evenly among each pita; roll up. Serve immediately.