01 - Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper and lightly grease.
02 - In a large bowl, combine rolled oats, all-purpose flour, light brown sugar, granulated sugar, baking powder, and salt. Add melted unsalted butter and mix until a crumbly texture forms.
03 - Reserve 1 cup of the oat mixture for the topping. Press the remaining mixture firmly and evenly into the prepared pan to create the crust.
04 - In a separate bowl, combine diced fresh strawberries, lemon juice, cornstarch, and granulated sugar. Stir gently to evenly coat the fruit.
05 - Spread the strawberry mixture evenly over the crust layer in the pan.
06 - Sprinkle the reserved oat mixture evenly over the strawberry filling.
07 - Bake for 35 to 38 minutes, or until the crumble topping is golden brown and the filling is bubbling.
08 - Allow the bars to cool completely in the pan. Lift out using parchment paper and cut into individual bars.