Preheat the oven to 350°F (175°C) and line a large baking sheet with parchment paper or a silicone baking mat.
In a large mixing bowl, mash the bananas with a fork until a smooth paste forms with minimal lumps.
Whisk in the almond butter, maple syrup, and vanilla extract until the wet ingredients are fully emulsified.
Stir in the rolled oats, ground cinnamon, and sea salt using a spatula until all oats are thoroughly coated.
Gently fold in the dark chocolate chips and chopped walnuts.
Using a 2-tablespoon scoop, portion the dough onto the prepared baking sheet, spacing them 2 inches apart.
Press down lightly on each mound to flatten into a disk shape, as these cookies do not spread during baking.
Bake for 12 to 15 minutes until the cookies feel firm to the touch and the bottoms are lightly browned.
Remove from the oven and let cool on the baking sheet for 10 minutes to set before serving.