Heat a large frying pan over high heat. Add the oil and lamb and cook for 5 minutes, stirring, or until golden brown. Add cumin and garlic and cook for another minute.
Heat up sandwich press. Place breads on a clean work surface. Top half of each bread with the lamb mixture, spinach and feta. Season with black pepper. Fold over each bread to form a half circle.
Cook two melts at a time in sandwich press until crisp and spinach wilted. Cut into wedges and serve sprinkled with sumac and accompanied with lemon wedges.