Shepherd's Pie with Ground Lamb and Sweet Potatoes

Preheat the oven to 450 degrees F (230 degrees C). Prick sweet potatoes several times with a fork and place onto a baking sheet.

Bake in the preheated oven until easily pierced with a fork, 50 minutes to 1 hour.

In the meantime, heat a large skillet over medium-high heat. Cook and stir lamb in the hot skillet until browned and crumbly, 5 to 7 minutes. Transfer to a plate.

Add onion, leek, and celery to the skillet and saute until tender, 4 to 5 minutes. Stir in tomato sauce, chickpeas, cumin, salt, and pepper. Reduce heat; simmer 5 to 10 minutes. Return lamb to the skillet and simmer for 1 to 2 minutes more.

Reduce oven temperature to 325 degrees F (165 degrees C). Pour lamb mixture into a baking pan. Mash the sweet potato in a bowl, stir in tahini and green onions, and spread on top of the lamb.

Bake in the preheated oven until bubbling throughout and top is lightly browned, about 40 minutes.