Preheat the oven to 200℃ (400℉) Gas mark 6. Line a 12-hole muffin tin with paper cases.
Place the chopped rhubarb in a roasting tin with 20g of caster sugar and bake for 10 minutes.
Meanwhile, make the topping by placing the oats and ground ginger into a bowl and rubbing in the butter until very crumbly, and then stir in the sugar.
Remove the rhubarb from the oven, spoon into a sieve and leave to drain.
Place the flour and baking powder into a large bowl with the remaining sugar.
Whisk together the eggs, milk, yoghurt and melted butter.
Stir the wet ingredients into the dry, stirring in the rhubarb and ginger towards the end of mixing - do not over mix, lumpy dough is best!
Spoon into the paper cases and sprinkle over the crumble topping.
Bake for 25 minutes, until risen and golden. Cool on a rack.