Prepare Mustard-Chive Cream Sauce.
Preheat oven to 350°.
Place bread in a food processor; pulse 10 times or until coarse crumbs measure 1 cup. Sprinkle 3/4 cup breadcrumbs on a baking sheet. Bake at 350° for 5 minutes or until golden; set aside.
Combine remaining 1/4 cup breadcrumbs, mashed potatoes, and next 7 ingredients in a medium bowl. Shape mixture into 8 small patties. Place toasted breadcrumbs on a plate or shallow dish. Dredge fish cakes in breadcrumbs and set aside.
Coat fish cakes on each side with cooking spray. Cook cakes in a medium nonstick skillet over medium-high heat 3 to 4 minutes on each side or until lightly browned. Top cakes with Mustard-Chive Cream Sauce.