Grilled Kofta Kebabs

Name: Grilled Kofta Kebabs
Ingredients: 1 medium onion; 1 slice bread (white or whole wheat); 2 tablespoons milk; 1 pound ground beef; 1 pound ground lamb; 1 cup fresh parsley, chopped; 1 teaspoon ground allspice; 1 teaspoon ground cumin; 1 teaspoon paprika; 1 teaspoon kosher salt; 1 teaspoon sumac; 1/2 teaspoon ground cinnamon; 1/2 teaspoon ground coriander; 1/4 teaspoon freshly ground black pepper; 2 cloves garlic, minced; Neutral oil, for the grill grates; 1 cup whole-milk yogurt; 1 tablespoon lemon juice; 1/2 teaspoon kosher salt; 1 clove garlic, grated; Warm pita, sliced tomatoes, fresh parsley leaves and thinly sliced onion, for serving