Preheat oven to 350 degrees F. Spray a 13 x 9 inch baking dish with nonstick cooking spray.
Prepare cake batter as directed on the box. Most yellow cake mixes require 3 eggs, 1/2 cup oil and 1 cup water. If you box's directions differ, follow the direction on the box.
Pour the prepared cake batter into the prepared baking dish; set aside.
In a small saucepan, heat rhubarb, orange juice and sugar to a simmer. Simmer for approximately 10 minutes or until thickened.
Remove from heat and stir in orange zest and butter.
Pour the rhubarb sauce over the prepared cake batter.
Bake for 30- 35 minutes or until set.
Cake can be eat as is or with optional glaze. To serve, cut the cake and flip slice over on a plate so the cake is on the bottom and the rhubarb sauce is on top. Scoop additional rhubarb over top if it sticks in the pan.