01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper and lightly grease the surface.
02 - In a large bowl, mix rolled oats, all-purpose flour, light brown sugar, granulated sugar, baking powder, and salt. Add melted unsalted butter and stir until the mixture is crumbly.
03 - Reserve 1 cup of the crumble mixture for topping. Press the remainder firmly and evenly into the bottom of the prepared pan to form a smooth crust.
04 - In a separate bowl, combine diced fresh strawberries, lemon juice, cornstarch, and granulated sugar. Stir gently to evenly coat the fruit.
05 - Evenly spread the strawberry filling over the pressed crust in the pan.
06 - Sprinkle the reserved crumble mixture evenly over the strawberry layer.
07 - Place pan in the oven and bake for 35 to 38 minutes until the topping is golden and the strawberry filling is bubbling at the edges.
08 - Allow to cool completely in the pan. Remove using the parchment paper and cut into bars for serving.