COMBINE pumpkin, water, concentrate, sugar, salt and cinnamon in large bowl; whisk until smooth. Pour into 8-inch-square baking pan; cover with plastic wrap. Freeze, stirring every 30 minutes to break up ice crystals, for 3 hours, or until slushy, more uniform in texture and firm enough to scrape or scoop. Using metal spoon or ice cream scoop, scrape into chilled serving dishes. Serve immediately. Freeze any remaining granita for up to 1 week. Let stand at room temperature for about 15 to 20 minutes before serving.
Tip: Broken up pieces of the frozen granita can be placed in a food processor to break up before serving.