Heat oven to 350℉. Lightly spray two, 13x9-inch bake dishes with cooking spray. Place 1/4 cup (4 tablespoons) of butter in each bake dish and pop the dishes into the oven to melt the butter (~5 minutes).
While the butter is melting, use a meat tenderizer, small pan, or hammer to gently pound the walnuts in the bag into smaller pieces for a rough "chop" but not too fine or to the point of becoming complete nut dust.
Remove the bake dishes from the oven. Divide and sprinkle the brown sugar evenly over butter in the pans. Arrange pineapple slices (10 slices per cake), cherries, and walnuts over the brown sugar layer.
In a large mixing bowl, add the cake mix, eggs, pineapple juice, and oil. Use an electric hand mixer to stir the ingredients on low for 30-40 seconds until combined. Increase hand mixer speed to medium-high and whip for 2 minutes until fluffy.
Divide batter between the bake dishes by gently pouring over the sugar-fruit layer.
Bake 40-45 min or until toothpick inserted into the center comes out clean. Remove bake dishes from the oven and allow to sit 5 minutes. Invert dish onto bake sheet or large serving platter to remove the cake from the bake dish.
Once individual servings are on dishes, drizzle each with 1 tablespoon caramel sauce and serve.
Notes
If the cake doesn't release straight away once inverted, give it a minute and the weight of the cake should pull it down.