Cut the dragon fruit in half. Scoop out the flesh with a spoon. Reserve the halves for serving, if desired. Freeze the halves until you are ready to fill them. Place the pulp of the dragon fruit in your food processor along with the water, lemon juice and sugar. Pulse until smooth. Pour into an ice cream maker and churn until frozen. Spoon the sorbet into the frozen halves, or freeze the sorbet until ready to serve.
Makes about 2 cups of sorbet.