Step 1Cut the rhubarb into half-inch pieces. In a medium, nonreactive saucepan, bring the rhubarb, two-thirds cup water and the sugar to a boil. Reduce the heat, cover and simmer until the rhubarb is tender and cooked through, about 5 minutes. Cool to room temperature.
Step 2Slice the strawberries and puree them in a blender or food processor with the cooked rhubarb mixture and lemon juice until smooth.
Step 3Chill the mixture thoroughly, then freeze in an ice cream maker according to the manufacturer's instructions.