Preheat your oven to 350°F (175°C) and line a 9x9-inch baking pan with parchment paper.

Combine the quick-cooking oats, all-purpose flour, light brown sugar, baking soda, and baking powder in a mixing bowl.

Add the melted unsalted butter to the dry ingredients and mix until the mixture resembles coarse crumbs.

Press about two-thirds of the crust mixture into the bottom of the prepared pan, then bake for 10 minutes.

Whisk together the sweetened condensed milk, frozen lemonade concentrate, egg yolks, lemon zest, and kosher salt until smooth.

Pour the filling over the pre-baked crust, spreading it evenly, then sprinkle the remaining crust mixture on top.

Bake for an additional 22-25 minutes, or until the top is lightly golden and filling is set.

Cool the bars in the pan at room temperature for at least 1 hour before slicing.