Preheat the oven to 190 degrees C. Trim the rhubarb and, if necessary, remove any tough stringy bits. Chop the rhubarb into 2–3cm pieces, then put the pieces in a bowl with the sugar, orange zest and juice. Toss together with your hands so the rhubarb is well coated in the sugary orange juice, then divide the mixture evenly among four shallow heatproof dishes.
Place the biscuits in a plastic bag, seal, then crush with a rolling pin or meat mallet until you have even crumbs. Combine the biscuit crumbs with the hazelnuts, then sprinkle evenly over the fruit.
Bake for 25–30 minutes, or until the fruit is tender and the topping is golden brown. Leave to cool for a few minutes before serving with cream or ice-cream.