Grilled Butterflied Leg of Lamb with Tahini-Mint Marinade

For the marinade, combine first 9 ingredients and 4 tablespoons water in a blender; process until smooth.

Place lamb in a nonreactive dish; add marinade. Turn to coat. Let stand at room temperature for 1 hour or refrigerate up to overnight. If refrigerated, let lamb return to room temperature before grilling.

Brush a grill with oil; heat to medium hot. Remove excess marinade from lamb. Grill until well browned, 12 to 16 minutes; turn and cook 12 to 16 minutes more, or until an instant-read thermometer registers 140 degrees in thickest part (for medium rare). Grill lemon slices for garnish. Transfer lamb to a cutting board; let stand 15 minutes. Cut into 1/4-inch-thick slices. Serve with grilled lemon and fresh mint.