Preheat the oven to 350 degrees F. Line two large baking sheets with parchment paper or silicone baking mats; set aside.
Mix the wet ingredients: In a large bowl, mash bananas with a fork, add in the nut butter, sourdough starter discard, maple syrup, egg yolk, melted butter, and vanilla extract. Mix until smooth and well combined; a few small banana chunks are okay.
Add the oat flour, baking soda, baking powder, ground cinnamon, and salt to the wet mixture. Stir until just combined. Fold in the rolled oats, chia seeds, sliced almonds, coconut flakes, and chocolate chips.
Use a medium cookie scoop to scoop the dough onto prepared baking sheets. With damp fingers, gently press the cookies down a bit until they are slightly flattened because they will not spread out during baking.
Bake for 10-12 minutes or until set. Remove from the oven and allow to cool on the pan for 5 minutes before transferring to a wire rack to cool completely. Top cookies with a pinch of flaky sea salt and enjoy!