In a mixing bowl, combine flour, baking soda, salt and cinnamon. Whisk to combine.
In a stand mixer (or a mixing bowl and hand mixer) cream together, melted coconut oil, brown sugar, egg, mashed bananas, and vanilla. Mix until light slightly fluffy. Add dry ingredients to the wet and mix just until combined. Add oats and mix again, just until the oats are evenly mixed.
Scoop the dough onto a cookie sheet. Bake in 350 degree oven for 9-11 minutes. If you like a more crisp edge, bake closer to 11 minutes.
When the cookies come out of the oven, use a drinking glass to shape the cookies into a perfectly round shape. Place the open end of the drinking class over the cookie and use a small circular motion to shape the cookie.
These store well in an airtight container for up to 5 days at room temperature. They can also be frozen for up to 3 months. Enjoy!