In a medium bowl, whisk together the millet flour, oats, tapioca starch, ground chia, baking powder, baking soda, and salt. Set aside.
In a large bowl, mix together the brown sugar with the butter until it is evenly mixed, then add the eggs, one at a time, followed by the maple syrup and vanilla.
Stir in the flour mixture, then the chocolate chips.
Cover and chill the dough overnight.
Preheat the oven to 350 °F (175 °C). Line a couple of baking sheets with parchment.
Scoop the dough with a tablespoon or ¾ oz scoop (like this one on Amazon), placing the scoops a couple of inches apart as the cookies spread.
Bake for 11 minutes and let cool on the cookie sheet a couple minutes before transferring as they are delicate when they first come out of the oven.
These are best eaten the day they are baked (especially when they are warm!).