Preheat the oven to 375°F. Line a small baking sheet with parchment paper.
In a small bowl, combine the ground flaxseed and water. Stir vigorously and then set aside for 5 minutes, allowing it to thicken/turn to a gel consistency.
In a medium bowl, combine the almond meal, salt, cinnamon (if using), and baking soda. Stir to combine. Then, add the flaxseed gel, maple syrup, tahini, avocado oil, and vanilla. Using a spatula, stir until the thick and slightly wet dough is combined and there are no dry spots.
Add the chocolate chunks to the cookie dough and fold them in until evenly distributed throughout.
Transfer the cookie dough to the baking sheet and press it out into an even circle that is uniformly 1-inch thick. Sprinkle the top of the cookie with flaky salt, cacao nibs, and sesame seeds.
Bake the grain-free tahini chocolate chunk cookie until the edges are browned and small cracks appear, about 10 minutes. Let the cookie cool completely (about 30 minutes) on the baking sheet before enjoying.