1. Preheat Oven: Preheat oven to 350°F (175°C). Line baking sheets with parchment paper.
2. Cream Butter and Sugars: In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
3. Add Eggs and Vanilla: Beat in the eggs one at a time, then stir in the vanilla extract.
4. Mix in Bananas: Stir in the mashed bananas until well combined.
5. Combine Dry Ingredients: In a separate bowl, whisk together the rolled oats, baking soda, cinnamon, and salt.
6. Add Dry Ingredients to Wet Ingredients: Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
7. Add Optional Ingredients: If desired, stir in chopped walnuts or chocolate chips.
8. Drop by Rounded Tablespoons: Drop by rounded tablespoons onto the prepared baking sheets.
9. Bake: Bake for 18-20 minutes, or until the edges are golden brown.
10. Cool: Let the cookies cool on the baking sheets for a few minutes before transferring them to a wire rack to cool completely.