Cinnamon Rhubarb Bread

Ingredients:
1 cup brown sugar, packed
2/3 cup vegetable oil
1 egg
1 teaspoon vanilla extract
1 cup buttermilk
2 1/2 cups all-purpose flour
1 teaspoon baking soda
1 teaspoon salt
1 1/2 cups rhubarb, diced
1/2 cup walnuts, chopped (optional)
1/2 cup sugar
1 teaspoon cinnamon
Directions:
Preheat Oven: