Preheat the oven to 350 degrees.
On a plate, mash your banana really well, using a fork.
In a large mixing bowl, cream together softened butter and brown sugar.
Add the mashed banana, the egg and vanilla, and stir to combine.
In a smaller mixing bowl, add the flour, baking soda, baking powder, salt, cinnamon, and nutmeg, whisking together well.
Combine the flour mixture with the butter mixture, mixing until just combined.
Add the bag of chocolate chips and mix well.
Using spoons or a cookie dough baller, spoon about 1.5 tablespoon sized balls of the dough onto baking sheets lined with parchment paper, placing each ball roughly 2" apart.
Bake for 9-12 minutes. These cook dark, making it difficult to tell if they're done or not. You aren't looking for golden brown in color. I slide a metal spatula under one cookie, and if it starts to lift without breaking, I remove them from the oven.
Let cool on the baking sheets for about 10 minutes before transferring to a wire rack. These cookies bake soft, and require more time to set fully.
Enjoy!