In a stand mixer (or large bowl with hand mixer), add softened butter and peeled banana. Mix on medium speed until the mixture is well combined and there are only a few small chunks of banana.
Add the vanilla extract and brown sugar and continue to blend until the mixture is light and fluffy.
In a separate medium bowl, whisk together the flour, baking soda and salt.
Slowly add these dry ingredients to the stand mixer while the mixer is running on low speed.
Add the rolled oats, pecans, and chocolate chips. Mix until just combined.
Using a spoon to scoop cookie dough into ~2" cookie dough balls.
Place 6 cookies on an 18x13" baking sheet in 3 rows of 2 cookies. You should have enough dough for two batches (12 large cookies total).
Bake for 15 minutes or until the cookies are slightly golden in color.
Remove from oven and allow to cool for 10 minutes before serving.