Clean, peel and cut the rhubarb into large pieces. Sort blueberries, wash and drain well. Peel bananas and cut them into slices. Mix oat flakes, coconut oil, honey, 4 tablespoons sugar, fruit and rhubarb.
Put the mixture into an ovenproof dish (approx. 1 1/2 l) and pour on the almond drink. Sprinkle with 1 tbsp. sugar. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: see manufacturer) for approx. 40 minutes. Remove Crumble from the oven and serve.