Lamb Stew with Lemon and Figs

Ingredients

1 1/2 cups plain whole-milk yogurt

3 tablespoons chopped fresh mint

1 2 1/2- to 3-pound boneless lamb shoulder, trimmed, cut into 1- to 1 1/2-inch cubes
2 tablespoons (or more) olive oil
2 onions (about 1 pound), thinly sliced
1 small lemon (preferably Meyer), ends trimmed, quartered lengthwise, thinly sliced crosswise
4 garlic cloves, minced
1 rounded teaspoon minced peeled fresh ginger
1/4 teaspoon ground cinnamon
1/8 teaspoon cayenne pepper
1 14 1/2-ounce can diced tomatoes in juice
1 cup dried figs, stems trimmed, quartered lengthwise (about 4 ounces)
2 1/2 cups (or more) low-salt chicken broth