Preheat the oven to 350°F (175°C), position a rack in the upper third, and one in the lower third of the oven. Line two baking sheets with parchment paper.
In a small bowl, combine the flour, oats, baking soda, baking powder, and kosher salt.
In the bowl of a stand mixer fitted with the paddle attachment, or in a large mixing bowl if you’re using a handheld mixer, combine the coconut oil and tahini. Add the sugar and mix until well combined. Crack in the eggs, one at a time, mixing well after each addition, when mixing at medium-high speed until the mixture is light. Mix in the vanilla extract. Add the flour mixture, mixing at low speed just until combined, then stir in the dark chocolate chips, macadamia nuts, and coconut.
Using a large ice cream or cookie scoop, drop the cookie dough onto the lined baking sheets, leaving a few inches between them because the cookies will spread quite a lot. Using a fork, flatten each cookie a bit, then sprinkle with additional coconut and flaky sea salt, if desired.
Place the first baking sheet on the top oven rack, and the second one on the lower rack. Bake for 10 minutes, then inverse the sheets, rotating them too. Bake for an additional 5 minutes, or until the edges barely start to turn golden and the center is still tender but set. Let cool on the pans for 5 minutes, then transfer to a rack to cool completely.
STORAGE
Store the cooled cookies in an airtight container at room temperature for up to 4 days.