Created by Christianna on August 23, 2012
Step 1: Preheat oven to 350 degrees F (175 degrees C). Grease a 9x13-inch baking pan.
Step 2: Mix rhubarb, sugar, strawberry gelatin mix, and tapioca in a bowl. Spread the rhubarb mixture into the bottom of the prepared baking pan.
Step 3: Beat the cake mix with water, vegetable oil, and eggs in a large mixing bowl until moistened; beat with an electric mixer on medium speed for 2 minutes. Pour the cake batter over the rhubarb mixture.
Step 4: Bake in the preheated oven until a toothpick inserted into the middle of the cake layer comes out clean, about 35 minutes. Let cake stand for 5 to 10 minutes before inverting on a plate.
Step 5: Serve warm with vanilla ice cream or whipped cream.