Preheat the oven to 180oC/Gas Mark 4.
Chop the rhubarb into roughly 4cm (11⁄2in) long pieces.
Place the rhubarb pieces onto a baking tray and scatter over the 50g (13⁄4oz) light muscovado sugar over the top. Bake for 10 minutes.
Place the oats, flour, sugar and coconut oil into a large bowl. Mix together, then rub the coconut oil into the dry ingredients until you have a crumbly consistency.
Tip the hot rhubarb into a pie dish. Add the grated ginger and orange zest and mix together. Top with the crumble mix, then bake for 35 minutes until the top is browned.
Serve with whipped coconut and vanilla cream, if desired.