Arayes Lebanese Crispy Meat Stuffed Pita

Name: Arayes (Lebanese Crispy Meat-Stuffed Pita)
Ingredients: 1/2 medium yellow onion; 6 sprigs fresh parsely; 3 cloves garlic; 1 tablespoon tomato paste; 1 tablespoon pomegranate molasses (optional); 1 tablespoon baharat spice; 1 1/2 teaspoons kosher salt; 1 teaspoon ground cumin; 1/2 teaspoon ground allspice; 1/2 teaspoon cayenne pepper (optional); 1 pound lean ground beef or ground lamb; 4 pocketed pita breads; 2 tablespoons olive oil; 1 clove garlic; 1 medium lemon; 1/2 cup plain Greek yogurt; 2 tablespoons tahini; 2 tablespoons water, plus more as needed; Kosher salt; Freshly ground black pepper; Sumac, for garnish (optional)