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; sesl. Marinate in refrigerator 2 hours, turning occasionally. Remove from bag; discard marinade.
Preheat oven to 350 degrees F.
Place lamb on a broiler pan; insert meat thermometer into thickest portion of lamb. Bake at 350 degrees for 1 hour or until thermometer registers 145 degrees (medium-rare) to 160 degrees (medium). Let stand 15 minutes. Slice lengthwise into thin strips.
Spread each pita with about 2 1/2 tablespoon Yogurt-Tahini Dip. Divide lamb, red onion, mint, tomato, and pickles evenly among each pita; roll up. Serve immediately.
397 cal, 10.7 g fat, 32.8 g pro, 42.1 g carb, 75 mg chol, 1117 mg sod.