Preheat oven to 400°F (200°C). Line a muffin tin with paper liners.
In a large bowl, whisk together the flours, sugar, baking powder, cinnamon, ginger, baking soda, and salt.
In a separate bowl, whisk the Greek yogurt, melted butter, eggs, and vanilla until smooth.
Add the wet ingredients to the dry ingredients and stir gently until just combined. Do not overmix. A slightly lumpy batter = better muffins.
Fold in the rhubarb until evenly distributed.
Divide batter evenly into muffin cups, filling about 3/4 full.
Mix topping ingredients and sprinkle over each muffin.
Bake for 18–22 minutes, or until a toothpick inserted in the centre comes out clean.
Cool slightly… or don’t. These are at their best still warm.