Pre-heat oven to 170ºC.
Place rhubarb in a saucepan with the cordial & water and gently simmer for 7-10 minutes till just cooked. Take off the heat and add the strawberries & blueberries and place in an oven-proof dish and keep warm.
For the crumble, whiz the flour, butter & sugar in a food processor until it crumbs, then mix in the oats & flaked almonds and place in a roasting tin and bake for 10-15 minutes. Then sprinkle on top of the fruit and serve.
The baked crumble mixture will keep in the fridge for at least a week and is delicious sprinkled on plain yoghurt.