Preheat oven to 375 F. Line two baking sheets with parchment paper. In a medium sized bowl, whisk to combine the flour, oats, cinnamon, baking powder, and salt. 

In the bowl of a hand held or stand mixer, cream the butter, sugars and vanilla until combined. Scrape down the sides of the bowl then add the egg and beat until smooth. Mix in the tahini. Turn the mixer to low speed and mix in the dry ingredients until just combined. Stir in the chopped chocolate with a wooden spoon. 

Use a cookie scoop to scoop the dough directly onto a baking sheet. Place them at least 2 inches apart. Bake for 8-11 minutes, until edges are light brown and the tops are set. Remove from oven and sprinkle with flaky sea salt (if desired). Allow to cool on the baking sheet for about five minutes then transfer cookies to a rack to cool completely.