Preheat your oven to 350°F (175°C). Line an 8x8-inch baking pan with parchment paper, leaving overhang on two sides for easy removal.
In a medium bowl, combine the chopped strawberries, granulated sugar, cornstarch, and lemon juice. Stir gently until the strawberries are evenly coated. Set aside while you prepare the crust.
In a large bowl, whisk together the flour, rolled oats, brown sugar, baking soda, and salt. Pour in the melted butter and vanilla extract, then stir with a fork until the mixture is evenly moistened and forms clumps. Reserve about 1/2 cup of this mixture for the topping.
Press the remaining crust mixture firmly and evenly into the bottom of the prepared pan. Spread the strawberry filling over the crust in an even layer. Sprinkle the reserved crumble mixture over the strawberries.
Bake for 28-32 minutes, or until the topping is golden brown and the strawberry filling is bubbly around the edges. Let the bars cool completely in the pan on a wire rack (about 1 hour) before slicing.
Once cooled, lift the bars out of the pan using the parchment overhang. Place on a cutting board and slice into 9 squares. Serve stacked on a plate, optionally with a dusting of powdered sugar or a scoop of vanilla ice cream.