Preheat the oven to 350°F (175°C). Line an 8x8-inch baking dish with parchment paper.
In a large bowl, mix flour, oats, sugar, baking soda, and salt. Stir in the melted butter until crumbly.
Press ⅔ of the mixture into the bottom of the prepared pan to form the crust.
Bake for 12–15 minutes or until lightly golden.
In a separate bowl, whisk together sweetened condensed milk, egg yolks, lemon juice, and zest.
Pour the lemon filling over the baked crust and spread evenly.
Crumble the remaining oat mixture on top.
Bake for another 15–18 minutes until the top is golden.
Let cool at room temperature, then refrigerate for at least 1 hour before slicing.