For burgers: 1 cup boiling-hot water 1/3 cup bulgur 3/4 teaspoon salt 1 medium onion, quartered 1/4 cup packed fresh cilantro leaves 1/4 cup packed fresh flat-leaf parsley leaves 1 lb ground lamb 1/2 teaspoon paprika (not hot) 1/4 teaspoon ground allspice 1/4 teaspoon black pepper 1/4 teaspoon cayenne
For sauce: 1 small garlic clove 1/8 teaspoon salt 1/2 cup walnuts (1 1/2 oz) 1/4 cup water 1 teaspoon fresh lemon juice 1/8 teaspoon cayenne
For pitas: 4 (4-inch) pita loaves 1 tablespoon olive oil Paprika (not hot) for dusting Garnish: fresh cilantro sprigs
Soak bulgur for burgers: Pour boiling-hot water over bulgur with 1/2 teaspoon salt in a small bowl and soak 15 minutes, then drain in a sieve.
Make sauce while bulgur soaks: Mince garlic and mash to a paste with salt (1/8 teaspoon) using a large heavy knife, then transfer to a food processor and blend with remaining sauce ingredients until smooth. Transfer to a bowl.
Prepare burgers: Preheat broiler. Pulse onion and herbs in cleaned processor until finely chopped, then transfer to a bowl and stir in bulgur, lamb, paprika, allspice, pepper, cayenne, and remaining 1/4 teaspoon salt until just combined. Form lamb mixture into 4 patties (4 inches in diameter).
Broil pitas and burgers: Arrange pitas on a baking sheet. Brush with oil, then lightly dust with paprika and season with pepper. Broil on lowest rack until toasted, 1 to 3 minutes (watch to prevent burning). Keep pitas warm, loosely covered with foil, while broiling burgers. Oil rack of a broiler pan and heat 4 inches from heat until hot, 3 to 5 minutes. Broil burgers, turning over once, until cooked through, 5 to 7 minutes total. Serve burgers on pitas, topped with sauce.
