Line a 4qt slow cooker with parchment paper and then a large piece of foil. Spray the foil lightly with nonstick cooking spray and set aside.
In a large bowl mix flour, all spice, baking soda, and salt, set aside. In a medium bowl stir together eggs, sugar, mashed bananas, vegetable oil, and vanilla. Add the banana mixture to the flour mixture and stir just until combined (do not over mix).
Add in chocolate chips and walnuts (optional) and pour into prepared slow cooker and cover. Cook on high for 4-1/2 to 5 hours, until a toothpick inserted comes out nearly clean. Remove from slow cooker by pulling out with foil and parchment paper.
(Optional) Using baking chocolate, melt in the microwave in 60-second increments, stirring between each increment until chocolate has melted and is smooth. Pour into a piping bag or Ziploc bag and snip one corner off. In know random pattern cover chocolate chip banana bread in melted chocolate and top with shaved white chocolate. Cut into pie shaped pieces and serve.