01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper and lightly grease the surface.
02 - In a large mixing bowl, combine rolled oats, all-purpose flour, light brown sugar, granulated sugar, baking powder, and salt. Pour in the melted butter and blend until the mixture forms coarse crumbs.
03 - Set aside 1 cup of the oat mixture for topping. Press the remaining mixture firmly and evenly into the prepared pan to create the crust base.
04 - In a separate bowl, mix diced strawberries with lemon juice, cornstarch, and granulated sugar. Stir gently until the fruit is evenly coated.
05 - Spoon the strawberry mixture evenly over the crust in the pan.
06 - Distribute the reserved oat crumble mixture evenly over the strawberry layer.
07 - Bake for 35–38 minutes, or until the oat crumble is golden brown and the filling is bubbling.
08 - Allow the bars to cool completely in the pan. Lift out using the parchment and slice into bars for serving.