1For the Banana Cake:
Preheat oven to 350 degrees. Grease two 9x11 1/2 cake rounds; set aside. Stir together flour, baking powder, baking soda and 1/2 teaspoon of salt; set aside.
In a large mixing bowl, beat butter with an electric mixer on medium to high speed for 30 seconds. Add sugar and vanilla beating until combined. Add eggs, one at time, beating between each to incorporate. Combine bananas and buttermilk. Add flour mixture and buttermik mixture, alternating starting and ending with flour, beating on low speed in between. Pour into cake rounds.
Bake at 350 degrees for 30 mins or until a wooden toothpick comes out clean. Cool for 10 minutes on a wire rack. Remove from pans and cool completely on wire racks.
2To assemble the cake:
Divide the cool whip topping in half. Add strawberries to half of the cool whip and the pineapple to the other half. In a small pot, heat and stir the fudge topping over low heat until just warm, not hot.
Use a serrated knife, cut the cake rounds in half horizontally. Place bottom of 1 split laye on serving dish. Top with the strawberry mixture, spreading to edge of te cake layer. Top with another layer of cake and spread with half of the fudge topping, letting it drizzle down the sides. Sprinkle with half of the chopped nuts. Top with another layer of cake and spread the pineapple mixture, spreading to the edge of the cake round. Top with last cake round and spread remaining warm fudge topping atop cake, letting it drizzle down the sides of the cake. Sprinkle with the remaining nuts. Serve immediately or cover loosely and chill up to 2 hours.