While the filling is chilling, whisk the brown sugar, egg, tahini, oil, vanilla, salt, cocoa, and water together in a large bowl. Add the baking soda and gluten-free flour and mix until a smooth dough forms. Chill the dough in the freezer for at least an hour.
Pour the raw sesame seeds into a bowl. Remove the chocolate filling from the fridge and the dough from the freezer. Scoop the dough directly into the bowl of sesame seeds, make a little well in the center of the dough ball, place one of the chocolate filling balls in the well, enclose the edges of the cookie dough around the chocolate ball, and lightly roll in the sesame seeds. Repeat with the remaining dough. Place all the sesame rolled, chocolate filled dough balls on a baking sheet lined with parchment and chill in the freezer.
Heat the oven to 350 degrees F (177 C). Once the oven is heated, remove the dough balls from the freezer, arrange 12 on one pan so that they won't bake into each other, and bake for 9-12 minutes or until the edges look slightly crackly. Let the cookies cool for at least 5 minutes before eating. Enjoy!
