Preheat your oven to 375°F (190°C). Line a 9x13 inch baking pan with parchment paper, leaving an overhang on the sides for easy removal.

In a large bowl, combine the flour, rolled oats, brown sugar, cinnamon, and salt for the crumble mixture. Whisk until evenly mixed.

Cut in the cold, cubed butter using a pastry blender or your fingertips until the mixture resembles coarse crumbs, with some pea-sized pieces remaining.

Reserve about 1 1/2 cups of the crumble mixture. Press the remaining crumble mixture firmly and evenly into the bottom of the prepared baking pan to form the base layer.

In a small bowl, gently stir together the apricot preserves and lemon juice to slightly thin the filling. Spread the apricot filling evenly over the base layer.

Sprinkle the reserved 1 1/2 cups of crumble mixture evenly over the apricot filling. Do not press down.

Bake for 35 to 40 minutes, or until the topping is golden brown and the filling is bubbly around the edges.

Allow the bars to cool completely in the pan on a wire rack (about 2 hours). Once cooled, use the parchment overhang to lift the slab out and slice into 12 bars.