Stir the honey, vinegar, cinnamon, ginger, citrus zest, cardamom, and red pepper flakes in a saucepan over medium heat until the mixture boils.
Add cranberries and red onions; bring to boil. Stir in rhubarb. Resist the urge to add any extra liquid--in a few minutes the rhubarb will release it's juice. Reduce heat to low and simmer until rhubarb is tender but not falling apart, about 4 minutes.
Cool to room temperature. Discard cinnamon.
Serve warm, or cover and refrigerate chutney until cold. It will keep about 2 weeks refrigerated. OR--can your chutney to enjoy later or give as gifts!
Refrigerated homemade chutney lasts about 2 weeks.