Remove the skin. Diver skin can taste pretty funky. If you want to add some fat and flavor, wrap it bacon.
Trim away any gristly areas on the underside of the breast.
Slice duck into finger-width strips. Combine soy sauce with next 4 ingredients in a medium bowl. Add duck and toss to coat. Cover and marinade for 2 – 4 hours. Remove from marinade and coat with mustard. Roll pieces in sesame seeds. Heat a thin layer of oil in a medium heat skillet. Add duck and brown lightly on all sides, about 3 – 4 minutes total cooking time. Remove duck and skewer with wooded skewers. Arrange on a platter and drizzle Spicy Mayonnaise over.