Preheat oven to 375 F (190 C). Grease or line a standard 12 cup muffin tin.
In a large bowl, add flour, flax, oats, sugar, baking soda, baking powder, and salt. Stir to combine.
In a medium bowl, beat egg. Add oil, mashed bananas, and vanilla. Stir to combine.
Pour wet ingredients into flour mixture. Add chocolate chips (or nuts) and stir just until moistened.
Divide evenly into prepared pan. Bake for 20-25 minutes, or until cake tester inserted into center comes out clean.
Notes
*If you don’t have ground flax seeds, just use an extra 1/4 cup of all purpose flour. **I often don’t measure the chocolate chips, a little extra can’t hurt right? You could also do a combination of chocolate and nuts, or omit them all completely.