In a large bowl, whisk together the butter, sugar, egg, tahini, cinnamon and vanilla until smooth.
Add in the baking soda, oat flour, salt and stir together with a rubber spatula.
Fold in the dates and half the chocolate and mix together. Save the remaining chocolate to press into the tops of the cookies before baking.
Chill the dough in the fridge for 1.5-2 hours
Preheat the oven to 350 F. Line a baking sheet with parchment paper and scoop out two tbsp worth of dough onto the pan. Repeat with remaining batter, making sure to leave at least 1 inch between each cookie.
Press the remaining chocolate pieces into the top of the cookies. Bake for 8-10 minutes, then remove the pan from the oven. You can tap the hot pan on the counter 1-2 times to flatten the cookies.
Let the cookies cool completely, then top them with flakey sea salt.
Keep stored in an airtight container for up to 2 weeks, or freeze for up to 6 months.