Preheat your oven to 350°F (175°C). Grease and line a 9x13 inch baking pan with parchment paper, leaving an overhang on the longer sides for easy removal.

In a large bowl, whisk together the flour, rolled oats, brown sugar, baking soda, and salt.

Cut the cold, cubed butter into the dry ingredients using a pastry blender or your fingertips until the mixture resembles coarse crumbs. Set aside about 1 1/2 cups of this mixture to use for the topping; this crumb mixture should be slightly looser than the rest.

Firmly press the remaining oat mixture evenly into the bottom of the prepared baking pan to form the base layer. Bake the base for 10 minutes until lightly golden.

While the base is baking, prepare the filling by stirring together the apricot preserves and lemon juice in a small bowl until smooth.

Remove the base from the oven. Spread the apricot filling evenly over the partially baked base.

Sprinkle the reserved oat mixture evenly over the apricot filling. Bake for an additional 30-35 minutes, or until the topping is golden brown and the filling is bubbly.

Let the bars cool completely in the pan on a wire rack (at least 2 hours) before lifting them out using the parchment paper overhang and slicing into 12 bars.