Preheat the oven to 350F. Line a baking sheet wtih parchment paper
In a stand mixer with the paddle attachment, beat together the butter, sugar, tahini, and maple syrup until white and fluffy, about 3-5 minutes. Add the egg and vanilla, and beat for another 2 minutes.
Add the oats, flour, baking powder, baking soda, and salt to the bowl. With a spatula, gently stir the dry ingredients on the top together, then fold into the dough until most of the dry ingredients are incorporated.
Pour in the chopped chocolate, then beat on low speed for about 30 seconds, until there are no more white specks and all the chocolate has been mixed in.
Using a medium ice cream scoop, form the dough into balls and place 6, evenly spaced out, per large baking sheet.
Bake for about 12-13 minutes, until the cookies have puffed up and the edges are dark. Pull out of hte oven and immediately sprinkly flakey sea salt, if using. Allow to cool for about 10 minutes in the pan, then transfer to a wire rack.