Preheat your oven to 350°F (175°C). Line a 9x9-inch baking pan with parchment paper, leaving some overhang for easy removal.

Prepare the base: In a large bowl, combine the rolled oats, flour, brown sugar, baking soda, and salt. Add the melted butter and vanilla extract, stirring until well combined.Press the mixture firmly into the prepared baking pan to form an even base layer.

Prepare the Strawberry Filling: In a medium bowl, combine the diced strawberries, granulated sugar, lemon juice, and cornstarch. Mix well to coat the strawberries evenly. Spread the strawberry mixture over the oat base in the pan.

Make the Crumb Topping: In another bowl, combine the oats, flour, brown sugar, ground cinnamon, and salt. Add the cold butter pieces and blend with a pastry cutter or your fingers until the mixture forms coarse crumbs.

Assemble and Bake: Sprinkle the crumb topping evenly over the strawberry filling. Bake in the preheated oven for 35-40 minutes or until the topping is golden brown and the filling is bubbly.

Cool and Serve: Allow the squares to cool completely in the pan on a wire rack. Once cooled, use the parchment paper overhang to lift the bars out of the pan. Cut into squares. Store in an airtight container in the refrigerator for up to one week.