In a medium bowl, whisk together dry ingredients - flours, baking powder, baking soda, salt and sugar.
In another medium bowl, mix together the wet ingredients (oil through vanilla). Add dry ingredients and stir until just combined, being careful not to over mix.
Gently fold in diced rhubarb and oats.
Fill muffin papers 3/4 full and bake for 15 minutes or until a toothpick entered into the center of a muffin comes out clean.