In a medium saucepan combine the chopped rhubarb, sugar, water, and lemon juice and heat over medium heat. Cook until the rhubarb is soft, about 10 to 12 minutes. Cool completely. This step can be completed the day before.
Slice the strawberries and combine with the cooled rhubarb. Using an immersible blender or a blender to process the ingredients until they are pureed.
Pour into a bread pan, cover with aluminum foil, and place in the freezer. Stir the ingredients for the first couple of hours about every 30 minutes, until the ingredients start to freeze completely