Combine finely chopped rhubarb and water. Simmer over medium heat for about 5 minutes. Add strawberries and vegan sugar. Simmer another 5 minutes. Puree mixture until smooth in a blender or food processor. Dehydrate in a dehydrator or in oven.*
To dry in an oven just set temp at lowest possible setting --about 140 degress would be good. Dry until fruit feels leather like ;yet pliable. This would probably best be done on parchment paper, Remove the leather while it is still warm and roll it up.