Cook 5 trimmed asparagus spears in salted boiling water until crisp-tender, 2 to 3 minutes. Drain and pat dry. Top one 4-inch piece lavash (or other flatbread) with the asparagus, 2 tablespoons shredded mozzarella, 1 tablespoon finely crumbled feta, 1/4 teaspoon za’atar (Middle Eastern spice blend), a few thin slices red onion and another piece of lavash. Brown in butter in a nonstick skillet over medium heat until crisp, about 2 minutes per side. Sprinkle with more za’atar.