Method

Filling

1. In saucepan, combine rhubarb (thaw and drain if using frozen) and water. Cook
   over medium high heat until rhubarb is tender (8 to 10 minutes).
2. In a small bowl mix cornstarch, sugar and cinnamon. Stir into rhubarb.
3. Continue cooking, stirring constantly until mixture boils and thickens.
4. Remove from heat and set aside.

Topping

1. In a small bowl, combine oats, cinnamon, four and brown sugar.
2. Add canola oil and stir until well distributed.
3. Set aside

Cake

1. Preheat oven to 350°F (180°C).
2. Spray a 9 x 13 (23 x33 cm) pan with canola oil.
3. In a large bowl, combine flours, baking powder, baking soda, salt, cinnamon.
4. In a large bowl with an electric mixer, lightly beat sugar, egg, canola oil, yogurt and vanilla. Mix well.
5. Gradually add flour mixture to wet mixture, beat until just combined. Batter will be fairly thick.
6. Spoon 2/3 of batter into the prepared pan.
7. Top with rhubarb filling.
8. Drop remaining batter on top of rhubarb.  There will be high and low spots and not all the rhubarb may be covered.
9. Sprinkle topping evenly over top of batter and rhubarb spots.
10. Bake for 40 to 45 minutes.
11. Cool cake on rack for 30 minutes