In a large mixing bowl, combine rhubarb, flours, brown sugar, baking soda an salt. In a separate bowl, blend together yogurt, oil and eggs. Stir into rhubarb mixture just until moistened. Fold in nuts. Spoon batter into 24 paper-lined muffin cups. Combine topping ingredients. Sprinkle a bit of topping mixture on the top of each muffin. Bake at 350 degrees for 20 to 25 minutes.
