Preheat your oven to 350°F (175°C).
Line your muffin tin with parchment paper or muffin liners.
In a mixing bowl, mash the ripe bananas until smooth.
In a separate bowl, whisk together the banana cake mix, all-purpose flour, instant banana pudding mix, and ground cinnamon.
In another bowl, beat the eggs, then add the mashed bananas, vegetable oil, water, and banana extract. Mix until well combined.
Gradually add the wet mixture to the dry ingredients. Stir gently until just combined.
Gently fold in the chopped walnuts.
Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.
Bake the muffins in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center comes out clean.
Once baked, let them cool in the tin for about 5 minutes, then transfer to a cooling rack.