Preheat oven to 325 degrees. In a bowl, whisk together flour, baking soda, baking powder and salt, set aside. Mash bananas on a plate with a fork and stir in lemon juice, set aside. In the bowl, using an electric mixer, whip together butter, sugar and sour cream until light and fluffy about 2 minutes.
Mix in egg and mashed bananas. Stir in dry ingredients alternating with buttermilk and mix until well incorporated. Pour mixture into buttered 8x8 baking dish and spread into an even layer.
Bake 45 minutes, or until toothpick inserted in center comes out clean. Remove from oven and allow to cool completely, at least one hour, and for prime cake at least 3 hours or overnight (this helps the cake to "ripen," you know how banana bread is always better later that day or the next. If cooling more than 1 hour cover with plastic wrap after 1 hour).
Once cake is cool, in a microwave safe bowl, combine chocolate chips and 1/4 cup heavy cream. Microwave on 50% in 30 second intervals stirring after each interval, until melted and smooth. Allow chocolate ganache to cool 5 minutes then pour, and spread evenly over cake.
Cover cake with plastic wrap and place on an even platform in freezer and freeze 20 minutes. Once cool, place a layer of sliced bananas evenly over cake (you will probably have a few extra that you can use to garnish top of cake slices).
In a mixing bowl, with an electric mixer, whip 1 cup heavy cream until soft peaks form then stir in powdered sugar. Whip until stiff peaks form. Dollop spoonfuls of whipped cream over cake and spread into an even layer.
Garnish with chopped pecans, cut into slices and garnish each slice with a banana and cherry if desired (cake topping tends to slide just a bit so if it does just use clean hands to keep the topping balanced, this is a banana split cake after all =). Store cake in refrigerator, note whipped cream will begin to separate after a few hours so this cake is best served immediately after frosted.
Note: I found this cake had cleaner cut slices after being refrigerated for 30 minutes, but you don't get that drippy chocolate so you decide =).