Preheat the oven to 325°F.
In a large bowl, mix the mashed bananas, eggs, and oil and set aside.
In another bowl, mix together the flour, baking soda, salt, sugar, and pudding mix.
Mix the dry ingredients into the bowl of wet ingredients, but avoid using a mixer. Do this part manually to keep the end result nice and fluffy.
Chop up the dark chocolate bar.
Add the chocolate, chopped walnuts and vanilla extract to the batter.
Grease the pan (this means rubbing lots of butter or vegetable oil all over it) or you can line the baking pan with parchment paper.
Bake until the cake bounces back when pressed or if a toothpick comes out clean when poked in. Depending on the pan, your baking time will vary. With a loaf pan (2 pans for this recipe), estimate around 60 to 80 minutes, depending on how deep it is.
Let it cool for about 10 minutes and flip it onto a clean plate or tray for serving.
Slice and serve it warm with butter or a scoop of ice cream! Keep it either refrigerated or left out in an airtight container.