In a large bowl, whisk together the flours, oats, flax seed, baking powder, salt, and ginger. Set aside.
In the bowl of an electric mixer, whisk the butter and brown sugar together until smooth. Add the eggs, one at a time, beating between each addition until smooth. Add the maple syrup, buttermilk, vanilla extract, and mashed bananas, and mix until combined.
With the mixer speed to low, gradually add the dry ingredients and mix just until the batter comes together. Add the chocolate chips, fruits, and nuts, and mix a few seconds, just to distribute evenly. (The batter will be thick.)
Using a ¼ cup (60 ml) measure or an ice cream scoop, drop dollops of batter on the baking sheets 2 inches apart. Using a fork, press down lightly on each batter mound to flatter into a cookie shape. Bake for 15 minutes, or until set and lightly golden around the edges. The cookies will not spread much and hold their form, but they puff up a little.
Let cool completely on a wire rack, then store in an airtight container in the refrigerator for up to a week, or in the freezer for up to three months.