Preheat the oven to 350 degrees F and line a muffin tin with liners for 12 muffins.
In a medium-large mixing bowl combine all your dry ingredients besides the walnuts. Then whisk in your egg, mashed bananas, and vanilla. (If you have a mixer use that, smooths everything really well!) Make sure everything is combined then gently mix in your chopped walnut pieces.
Evenly divide your batter in all of the muffin tins (they should be about 3/4 full or a tad bit more) and let them bake for about 20-24 minutes or until they're cooked through and golden brown (I check with a toothpick).
Let cool for at least 5-10 minutes and enjoy.