Trim excess fat and gristle from the lamb leg.

Lay the lamb flat on a cutting board.

Butterfly the thick ends to create an even thickness.

Score both sides of the lamb in a 1-inch crosshatch pattern.

Toast coriander and cumin seeds in a pan until fragrant.

Grind the toasted seeds with sesame seeds.

Combine ground spices with sumac, salt, and cinnamon.

Make a garlic paste with canola oil and rub into the lamb.

Rub the spice mix evenly into the lamb.

Let the lamb marinate for at least 1 hour at room temperature, or up to 1 day refrigerated.

Combine yogurt, chives, cilantro, dill, olive oil, lemon juice, salt, and cayenne in a bowl to make the herbed yogurt.

Preheat the grill to medium-high heat.

Grill the lamb over medium-high heat for about 5 minutes on the first side, watching for flare-ups.

Flip and cook for another 5 minutes.

Continue cooking, flipping every minute, until the lamb reaches 125 degrees F for medium-rare (about 5 minutes more).

Let the lamb rest for at least 5 minutes before slicing.

Slice the lamb thinly across the grain.

Serve with herbed yogurt.