MAKE THE ROSE RHUBARB
In a heavy saucepan, add 1 1/4 cup of the rhubarb, reserving 1/2 for later. Add the water, sugar and salt and simmer on medium heat uncovered for about 8 minutes, until the rhubarb is tender.
Carefully place the rhubarb mixture in a food processor and mix until smooth.
Return the sauce to the pan, adding the reserved 1/2 cup of rhubarb, plus one tablespoon of water. Simmer on medium low heat until the rhubarb is tender, about 5 or 6 minutes. You can add a bit more water during this process if the mixture gets too thick. Once it's done, stir in the rosewater and set aside to cool.
MAKE THE COCONUT MILK RICE PUDDING
In a 2 quart heavy saucepan, combine the water, butter, salt and zest and bring to a boil. Stir in the rice and return to a boil, then cover and lower the temperature to simmer over low heat until the water is absorbed, about 15-20 minutes.
In another large, heavy saucepan, combine the coconut milk, sugar, and vanilla bean and simmer on low heat. Add the rice mixture, and continue to simmer uncovered until most of the liquid is absorbed, about 15-20 minutes, stirring occasionally. Remove vanilla bean and sprinkle with cinnamon or top with Rose Rhubarb sauce before serving.
Note: This recipe serves 6-8, and it keeps well in the fridge for several days. The Rose Rhubarb sauce makes enough for a scant tablespoon of topping for each serving - but it's easily doubled if you want a more generous portion of rhubarb.