Preheat your oven to 350 degrees.
Spread the crushed strawberries on the bottom of a 9x13 baking dish. Evenly cover the strawberry jello powder over the berries. Top with the mini marshmallows.
Prepare the cake mix according to the back of the box. Pour the cake batter over top of the marshmallows. Bake in the preheated oven for 45 minutes, or until a toothpick inserted into the center comes out clean.
Cool in the pan for 15 minutes. Run a knife alongside the edge of the pan to loosen the sides. Turn the cake upside down onto a rectangle cake plate, tray, or sheet pan.
I like to serve mine with whipped cream.
Store the cake in the refrigerator.