
Preheat the oven to 350 ℉. Grease a 9x13" baking pan (or a 9" round springform pan.)
Spread out the chopped rhubarb on the bottom of the baking dish. Then sprinkle the sugar and gelatin over top, making sure it's all evenly distributed.
Cover the rhubarb and sugar with the contents of the yellow cake mix. Pour the water and then the melted butter over the cake mix, but DO NOT STIR. Then sprinkle the cinnamon and nutmeg on top of that. Bake for 45-50 minutes until the rhubarb is cooked through and tender and soft. Cool slightly before serving.