Preheat oven to 325°F. Grease a muffin tin or line with paper liners.
Combine the flour, baking soda, cinnamon, and salt in a large bowl.
Add the bananas, vanilla extract, sugar, oil, and eggs to a blender and blend until smooth. (Alternatively, you can mash the bananas with a fork and whisk this all together.)
Slowly stir the wet ingredients into the dry ingredients and mix until just combined. Fold in the berries. (If using strawberries, roughly chop them first.)
Fill each cavity of the prepared muffin tin about 3/4 of the way and bake for 25 minutes.
Allow the muffins to cool slightly before removing from the tin.