Preheat your oven to 180°C/350°F/gas 4.
Chop the rhubarb into small bite sized pieces. Put the rhubarb and half the sugar into a pan. Add the orange juice and zest, put a lid on top, bring to the boil and simmer for a few minutes. Remove the lid and simmer for around five more minutes, until the rhubarb has softened slightly.
Spoon into an ovenproof baking dish or individual dishes and spread out evenly across the bottom.
To make your crumble topping, use your fingers to lightly rub together the flour and butter until the mixture resembles fine breadcrumbs.
Stir in the oats, the rest of the sugar and the stem ginger.
Sprinkle the crumbs over the rhubarb and bake in the preheated oven for 40 to 45 minutes until the rhubarb is bubbling up and the crumble is golden.
If you like, you can make the crumble topping in a food processor. Just combine the flour, butter, sugar and stem ginger and whiz up. Add the oats for the last ten seconds.