Preheat oven to 350 F. Cream together margarine and sugar. Add egg whites and mix thoroughly. Combine dry ingredients and add the above alternately with milk. Stir in lemon rind and nuts. Bake in a lightly oiled 9 inch by 5 inch loaf pan for 60 minutes or until wooden pick inserted in center comes out clean. Remove bread from oven. Mix 1/3 cup powdered sugar with 3 tablespoons fresh lemon juice until smooth and pour over warm bread. Allow to sit for 20 minutes, then remove bread from pan.