Top-ranked recipe named "Easy Strawberry Jello Swirl Cake"
Follow yellow cake mix instructions as directed on the box (I believe I used pillsbury). Be sure to bake in a 13x9" pan.
While the cake is baking, prepare the jello as directed on the package.
Once you take the cake out of the oven, prick the entire cake generously with a toothpick. Pour (or ladle) the prepared jello liquid over the entire cake as evenly as possible. Refrigerate cake until cold, cut & serve. When you cut into the cake it will be marbled with the pink/red jello.
It's not exactly gourmet, but kids & adults both seem to enjoy it & it's simple!