Preheat your oven to 350°F and line an 8×8-inch pan with parchment, letting edges hang over for easy bar removal later.

In a large bowl, whisk old-fashioned oats, whole wheat flour, baking powder, cinnamon, and fine sea salt until evenly mixed with no clumps.

Stir in tahini, honey, and vanilla extract to the dry mix until moist crumbs form.

Press the mixture firmly into the prepared pan, using a spatula or damp fingers to level and compact it.

Bake at 350°F for about 20 minutes, until edges turn golden brown and the center feels set but still slightly tender.

Melt dark chocolate and coconut oil in a heatproof bowl over simmering water, stirring until silky smooth.

Spread the melted chocolate evenly over the baked oat base.

Chill the bars in the refrigerator for at least 1 hour.

Slice the chilled bars into squares, wiping your knife between cuts and topping with flaky sea salt.