Preheat the oven to 350 F.
Line two cookie sheets with parchment paper.
In a medium bowl, whisk together the flour and baking powder.
Pulse the oats in a food processor until coarse. Add to the dry ingredients.
Add the butter, brown sugar, peanut butter, and vanilla to the bowl of a stand mixer or a stand-alone bowl with a hand-held mixer.
Beat together at medium speed until well combined, about 5 minutes.
Add the mashed banana and stir well.
Add the dry ingredients and beat on low speed until the dough pulls together.
Stir in the chopped peanuts and trail mix.
Drop cookie dough by heaping teaspoons. Keep each cookie spaced about 2 inches apart.
Bake for 8-10 minutes, then cool on a wire baking rack.
Enjoy!
