To make this Fresh Strawberry Upside Down Cake gluten-free. Simply substitute the yellow cake mix. With a gluten-free cake mix. Ensure that all other ingredients. Including the strawberry Jell-O and marshmallows Are also gluten-free (most brands are, but it's always good to check). Follow the same instructions for preparation. And baking. The result will be just as delicious. With all the layers of flavors. And textures intact. Making it a perfect dessert. For those with gluten sensitivities. Or preferences.