1. Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving some overhang for easy lifting.
2. In a medium bowl, whisk the flour, coconut sugar, graham cracker crumbs, baking soda, baking powder, and salt.
3. Smash the banana and add it to the bowl with the flour along with the melted butter, and vanilla. Stir the cookie dough mixture until just combined, then fold in the chocolate chips.
4. Press half of the cookie dough evenly into the prepared pan. Dollop marshmallow fluff across the surface (it doesn’t have to fully cover) and then crumble the remaining cookie dough over top of the marshmallow fluff, leaving some marshmallow that peeks through.
5. Bake for 20–22 minutes, or until golden at the edges and set in the center. Cool in the pan for 20 minutes before lifting out and slicing into bars.

Storage

Store covered at room temperature for up to 2 days or in the fridge for up to 4 days. You can also freeze them for up to a month — just thaw at room temperature before serving.