Palestinian Lamb Stew with Sumac Chard and Chickpeas

Name: Palestinian Lamb Stew with Sumac, Chard, and Chickpeas
Ingredients: 1½ lb. boneless leg of lamb, cut into 1-in. pieces; 1 tsp. whole allspice berries; 1 tsp. black peppercorns; 5 green cardamom pods; 1 bay leaf; 1 cinnamon stick; 1 medium yellow onion, coarsely chopped; ½ cup sumac berries, or ⅓ cup ground (see headnote); 3 Tbsp. all-purpose flour; 2 Tbsp. extra-virgin olive oil, plus more for serving; 1 medium yellow onion, chopped; 1 lb. rainbow chard, thick stems discarded, sliced into ¼-in.-thick ribbons; One 15-oz. can chickpeas, drained, or 1½ cups cooked dried chickpeas; Fine salt; 1 Tbsp. dill seeds; 1½ tsp. crushed red chile flakes; 5 garlic cloves; 2 green chile peppers, such as serrano, finely chopped (see headnote); 2 Tbsp. coarsely ground sumac, preferably Al-Ard brand, plus more for garnish; 1 tsp. ground coriander seeds; 3 Tbsp. roasted sesame tahini, or regular tahini (see headnote); Ground Aleppo pepper (optional) and sumac, for serving