Yogurt-Marinated Chicken Shawarma

Ingredients

• 2 lb. boneless, skinless chicken thighs, cut into 1-inch cubes
• 1 3⁄4 cups full-fat Greek yogurt
• 1⁄2 cup plus 2 tbsp. olive oil
• 1 tbsp. freshly ground black pepper, plus more to taste
• 1 tbsp. ground allspice
• 1 1⁄2 tsp. ground coriander
• 1 1⁄2 tsp. ground cumin
• 1 tsp. cinnamon
• 1 tsp. kosher salt, plus more to taste
• 8 cloves garlic, minced
• 1 small white onion, grated
• Skewers, for grilling
• 4 pita breads
• 1 tbsp. fresh lemon juice
• 1⁄2 cup minced cucumber
• 1⁄2 cup frozen, thawed, chopped spinach
• 2 tbsp. minced fresh dill
• 2 tbsp. minced fresh mint
• 2 tbsp. minced fresh parsley
• 1 tsp. dried mint
• 1⁄2 bulb fennel, outer layers discarded, cored and finely chopped
• Sumac, for garnish