Cook noodles in a 4-quart pot of boiling salted water until just tender, 2 to 3 minutes. Drain in a colander, then rinse under cold water and drain well. Stir together vinegar, sugar, and salt in a bowl until sugar is dissolved, then add noodles and toss well.
Heat 1 tablespoon oil in a 10- to 12-inch heavy skillet over moderately high heat until hot but not smoking, then sauté duck pieces, starting with skin sides down and turning occasionally, until skin and meat are crisp, 3 to 5 minutes. Transfer with tongs to a cutting board. (Do not clean skillet.)
When duck is cool enough to handle, remove crisp skin from meat and thinly slice skin. Remove and discard any excess fat from meat, then shred meat into 1/4-inch-wide pieces.
Heat remaining 1/4 cup oil in skillet over moderately high heat until hot but not smoking, then fry shallot, stirring occasionally, until golden brown, about 2 minutes (watch closely, as shallot can burn easily). Quickly transfer with a slotted spoon to paper towels to drain.
Working around core of cucumber, cut thin lengthwise slices (about 1/8 inch thick) with slicer, then stack slices. Halve stack crosswise, then cut slices lengthwise into 1/4-inch-wide matchsticks.
Cut each peach half lengthwise into 1/8-inch-thick wedges with slicer or a sharp knife.
Put 1 lettuce leaf on each of 6 plates, then divide noodles among leaves and top with duck (meat and skin), cucumber, peach, shallot, and herbs. To eat, roll lettuce leaf into a cylinder to enclose filling.