01 - Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper and lightly grease.
02 - In a large bowl, mix oats, all-purpose flour, light brown sugar, granulated sugar, baking powder, and salt. Pour in melted butter and blend until crumbly.
03 - Set aside 1 cup of the oat mixture for topping. Press the remaining mixture firmly and evenly into the prepared pan.
04 - In a separate bowl, toss diced strawberries with lemon juice, cornstarch, and granulated sugar to coat the fruit evenly.
05 - Evenly spread the strawberry mixture over the oat crust.
06 - Sprinkle the reserved crumble mixture evenly over the strawberry layer.
07 - Bake for 35 to 38 minutes, or until the topping is golden and the filling is bubbling.
08 - Allow bars to cool completely in the pan before lifting out and cutting into portions.