1. Preheat oven to 375°.
2. Combine ice cream and cinnamon in a bowl; cover and freeze at least 30 minutes.
3. While ice cream freezes, combine rhubarb and next 3 ingredients in an 11 x 7-inch baking dish; stir well to dissolve sugar. Bake at 375° for 30 minutes or until rhubarb is soft, stirring once during cooking. Let stand 10 minutes to cool. Serve with cinnamon ice cream.