In a bowl, beat brown sugar, oil and egg. Add buttermilk, vanilla and baking soda; mix well. Combine flour, salt and cinnamon; stir into milk mixture. Fold in rhubarb and nuts if desired. Pour into two greased 8x4-in. loaf pans. Combine topping ingredients' sprinkle over loaves. Bake at 350° for 1 hour or until bread tests done.