01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a large bowl, cream together the butter, brown sugar, and granulated sugar until light and fluffy.
03 - Beat in the mashed bananas, egg, and vanilla extract until well combined.
04 - In a separate bowl, whisk together the flour, baking soda, salt, cinnamon, and nutmeg.
05 - Gradually add the dry ingredients to the wet mixture, mixing just until incorporated.
06 - Stir in the oats, raisins, and nuts (if using) with a spatula until evenly distributed.
07 - Drop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart.
08 - Bake for 11 to 13 minutes or until the edges are golden brown and the centers look set.
09 - Cool on the baking sheets for 5 minutes, then transfer to a wire rack to cool completely.