First you have to mix mustard with just enough hot water to make a pasteand than set aside. After that, combine soy sauce, sherry, chicken broth and sugar in a saucepan and simmer over low heat.
Add cornstarch and cook, stirring constantly, until mixture thickens.and than set aside. Preheat barbecue to medium-high. Coat fish with oil, place in a grilling basket and brush with about 4 tablespoons of glaze. Grill skinned side down 6-8 minutes, basting with glaze. Mix remaining glaze with mustard and spoon a little onto each fish. Garnish with parsley.
*Brands may vary by region; substitute a similar product.