In small pan, stir sesame seeds over low heat until tan, about 5 minutes. Place 1 tablespoon in suribachi or mortar and crush fine. Blend in lemon zest, juice, oil, shoyu, marmalade, ginger, and water. (Alternatively, combine the ingredients in a blender; whirl to blend and puree as smooth as possible.) Spoon over the hot mustard. Sprinkle with remaining sesame seeds. Serve at once.