Preheat oven to 375 degrees F (190 degrees C). Grease 12 muffin cups or line with paper muffin liners.
In a medium bowl, combine flour, baking powder, baking soda, salt and cinnamon. In a separate bowl, whisk together eggs, sugar, oil and vanilla extract. Add the mashed banana and mix until blended.
Add the wet ingredients to the dry ingredients and mix until just blended. Do not over mix. Fold in the walnuts and blueberries.
Fill muffin cups about 3/4 full with batter. Bake for 18 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Let cool for 5 minutes before removing from pan. Serve warm or at room temperature.
Interesting Facts
Bananas are a great source of potassium, vitamin B6 and vitamin C.
Walnuts are an excellent source of omega-3 fatty acids.
Blueberries are an excellent source of dietary fiber and antioxidants.