Preheat your oven to 350°F (175°C).
Line your baking sheet with parchment paper to prevent sticking and for easy cleanup.
In a large mixing bowl, combine the rolled oats, whole wheat pastry flour, ground flaxseed, light brown sugar, baking powder, baking soda, ground cinnamon, and salt. Stir well.
In another bowl, mash the ripe bananas until smooth. Add the beaten egg, melted coconut oil, melted unsalted butter, buttermilk, and vanilla extract. Mix until well combined.
Pour the wet mixture into the dry ingredients and stir until just combined, being careful not to overmix.
Gently fold in the fresh blueberries, toasted sliced almonds, and chopped dark chocolate.
Using a tablespoon or cookie scoop, drop heaping tablespoons of cookie dough onto the prepared baking sheet, spacing about 2 inches apart.
Bake for 12-15 minutes or until the edges are lightly golden. Watch carefully to avoid overbaking.
Remove from oven and let cookies cool on the baking sheet for about 5 minutes before transferring to a wire rack to cool completely.