Grease one 13x9x2-inch baking pan. Set pan a side.
In a large bowl blend together just until moist, the cake mix, the water (or the reserved pineapple juice), softened butter, and eggs. Then beat on medium speed for 2 minutes. Set bowl a side.
In a medium size bowl mix together by hand, the rhubarb, crushed pineapple, granulated sugar and brown sugar, plus the strawberry jell-o.
Pour the rhubarb mixture into the already greased baking pan. Spread mixture evenly in pan.
Now pour the cake batter over the rhubarb mixture. Using the back-side of a tablespoon; spread the cake batter evenly over the rhubarb mixture.
Bake in oven for 55 minutes. Cake should look golden brown in color when done baking. If need be, do the toothpick test in center of cake, to be sure cake is done baking. (Mine was done baking within 55 minutes.)
Let cake sit to cool down a bit before serving. Either serve cake while it's still warm, or cool completely then serve. Or refrigerate to serve later. (Refigerate any leftover cake.)
Top cake with a dollop of Cool Whip, or with a bit of Reddi Wip Whipped Topping.
*Note: Be sure to thoroughly drain the juice from the canned pineapple. I use a mesh colander to drain the pineapple in, plus I press down the crushed pineapple with a spoon. From that, I got exactly 1-cup of juice to add to the cake mix, instead of adding water.
Also, the canned crushed pineapple I used, stated on the label... Natural Juice No Sugar Added, and the brand I used was... Liberty Gold.