Add all ingredients to a 6 quart or larger slow cooker and stir to combine.
Cover and cook on LOW heat for 5 hours.
Remove lid and and using tongs or a fork, fish out the cinnamon stick and discard.
Serve warm strawberry rhubarb sauce over ice cream or angel food cake OR spoon sauce into a food safe container and chill in the refrigerator for up to 2 weeks.
Notes
This sauce will be a little on the tart side using 1 cup of sugar. If you would like your sauce to be sweeter you can increase the sugar to suit your tastes using up to 2 cups total of sugar.If you are watching your sugar intake feel free to use other sweeteners such as Stevia, Monk Fruit, Sucralose, etc.