In food processor, process walnuts, breadcrumbs, lemon rind, oil, dill and salt and pepper to taste, using pulsing action until crumbly [mixture should slightly stick together]; set aside.
Place salmon fillets skin side down, and brush tops with mustard. Divide crust mixture evenly among fillets; press onto mustard. Cover with plastic wrap and refrigerate at least 15 minutes or up to 2 hours.
Place salmon fillets on baking pan. Bake at 350°F [180°C] about 15 minutes or until salmon flakes with fork. Drizzle with a little lemon juice.