Spray the inside of a 6 quart or larger slow cooker stoneware insert with non-stick cooking spray and set aside.
In bowl, whisk together the dry cake mix, eggs, vegetable oil and mashed bananas.
Pour batter into prepared slow cooker, using a silicone spatula to scrape the batter out of the bowl.. Spread the batter evenly.
Place a layer of paper towels or a clean flour sack type kitchen towel between the lid of the slow cooker and insert.
Cook on HIGH for 1 hour to 1 hour and 20 minutes or until a toothpick inserted in the middle of the cake comes out clean.
Dust with powder sugar if desired before serving.
I like to serve this cake dusted with a little bit of powdered sugar before serving. But you can also frost the cake with your favorite frosting (chocolate frosting is great!) or top your cake with fresh fruit such as sliced strawberries.