In a medium bowl, stir together the sugar, milk, oil, egg and vanilla. In a separate bowl, combine the flour, baking powder and salt. Add the dry ingredients to the wet ingredients and stir until just combined.
Fold the rhubarb gently into the batter.
Pour the bread batter into a greased and floured 9"x5" bread pan.
Make the crumble by mixing together the flour, sugar and butter in a small bowl. This mixture will be crumbly.
Spread the crumbs on top of the bread batter in the pan.
Bake at 350 degrees for 55-60 minutes. A toothpick inserted in the center of the bread should come out clean. Allow the bread to cool for 10 minutes, then remove the bread to a wire rack to cool completely.
Store at room temperature in an airtight container.