Chop your rhubarb and strawberries up and place in a large oven proof dish, I used around 6/7 stalks of rhubarb and the whole punnet of strawberries (except for a few which escaped as snacks).
Cover in a little bit of granulated sugar. Rhubarb can be quite sharp, but combined with the sweet strawberries, these two are a good combination.
Make your crumble topping! I do this in the food processor or it can be rubbed through with your hands. A basic crumble topping includes 100g of butter, 150gs of flour, plus some oats (around 80g). I also added muesli and some almonds to mine. Anything similar can be added to your crumble topping including the likes of sunflower seeds, brown sugar, cinnamon or orange zest. It should have a crumbly appearance. If it seems very dry, add some more butter!
Spread thinly over your fruit and sugar, and place into a preheated over for 40minutes. I normally place the crumble onto a baking tray and then into the oven, as sometime the fruit within the crumble can boil out the sides during cooking. The crumble will turn golden and the fruit will have soften once cooked. Serve alone, or with custard or cream.