Position a rack in the upper third of the oven and preheat to 375ºF. Line two large baking sheets with parchment paper.
In a large bowl, stir together the tahini, maple syrup, coconut oil, and vanilla. Sift in the oat flour, rice flour, baking soda, and fine sea salt and stir to combine. Stir in the oats and chocolate.
Scoop dough balls 1 inch in diameter (about 3 tablespoonfuls or a 24 spring-loaded ice cream scoop) onto the prepared baking sheets, spacing them 2 to 3 inches apart. Top each cookie with a chunk or two of chocolate and a tiny pinch of flaky sea salt. Bake one baking sheet at a time, rotating halfway through for even baking, until the edges are pale golden and the centers are still soft, 8 to 10 minutes. Slide the cookies, parchment and all, off of the baking sheet and onto a cooling rack to stop the baking. Repeat to bake and cool the remaining cookies. Enjoy warm or let cool completely.