Preheat the oven to 350°F (177°C) and line a standard 12-cup muffin pan with paper liners.
In a large mixing bowl, mash the ripe bananas until smooth, then add the banana cake mix, instant banana pudding mix, all-purpose flour, and ground cinnamon.
Add the eggs, vegetable oil, water, and banana extract to the dry ingredients and beat with an electric mixer on medium speed until the batter is smooth, about 3 to 4 minutes.
Fold in the chopped walnuts until evenly distributed.
Spoon the batter into the prepared muffin cups, filling each about three-quarters full.
Bake in the preheated oven for about 20 minutes, or until a toothpick inserted into a muffin center comes out clean.
Let the muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.