Heat the oven to 180°C (160° fan) gas 4.
Butter a baking dish.
For the filling
Mix together the rhubarb, cranberries, sugar and orange juice.
Put into the baking dish.
For the crumble
Mix all the ingredients together until crumbly.
Sprinkle over the fruit.
Bake for 20-25 minutes until the rhubarb is tender and the crumble is golden.