Preheat the oven to 350°F. Spread the walnuts in a single layer on a baking sheet. Toast for 6-8 minutes, then cool completely.
Sift together the both flours, pudding mix, baking powder, baking soda and salt. Set aside.
In the bowl of a stand mixer cream together the softened butter, sugar and vanilla until pale yellow and fluffy. Around 3 minutes. Add the eggs one at a time beating well after each addition. Stop the mixer and scrape the sides of the bowl as needed.
To the bowl add the sifted dry ingredients to the creamed mixture alternately with the buttermilk.
After all of the ingredients have been added increase the mixer speed and beat for 1 minute or just until fully combined. Stop to scrape the side of the bowl and the beater as needed.
By hand, mix in 1 1/4 cup milk chocolate chips, 1 1/2 cup toasted walnuts and cubed banana into the batter.
Spray a standard 12-14 cup bundt pan with baking spray, then spread the thick batter into the pan.
Bake for 45-55 minutes, or until a tester inserted into the center comes back clean.
Cover the top with aluminum foil to prevent over-browning, if needed. Cool completely in the pan then invert onto a cake plate.
Milk Chocolate Drizzle: Melt together 3/4 cup chocolate chips and heavy cream in a microwave safe bowl. Heat in 20 second increments stopping to stir each time. Repeat process until completely smooth.
Drizzle glaze over cooled cake and sprinkle the top with reserved toasted walnuts.