Rough chop garlic cloves, fresh herbs, and scallions, then add to bowl of food processor along with lemon zest, lemon juice, salt, and black pepper. Pulse until finely chopped.

With processor running, drizzle in olive oil.

Pour pesto into a bowl and set aside.

Lay out leg of lamb, and spread open to a single layer.

Use paper towels to pat dry.

Trim any excess fat.

Apply an even coating of pesto to all surfaces of the lamb.

Fold lamb back up, place in a large pan, and cover with plastic wrap.

Refrigerate for a minimum of 2 hours and up to overnight.

Remove lamb from refrigerator and let rest on counter (still covered and wrapped) for one hour to take the chill off.

Preheat all burners of the grill on High for 15 or 20 minutes.

The lamb will cook on indirect heat.

Just before adding lamb, turn off appropriate burners and turn remaining burners to Low.

Open lamb to a single layer and place, fat side up, on the indirect heat.

Add probe thermometer to thickest part of the lamb.

Grill for 30-40 minutes.

Flip.

Cook until probe thermometer reads 125 degrees F.

(total cooking time should be 75-90 minutes)

Remove from grill.

Tent loosely with foil and let rest for 20 minutes before carving.