In a saucepan over medium heat, combine the crushed strawberries, lemon juice, cornflour, and sugar. Stir constantly until the mixture have thickened. Set aside.

Preheat the oven to 180C/350F/Gas 4. Line an 8x8-inch square baking pan with aluminium foil, and spray with baking spray. Set aside.

Whisk together the flour, baking powder, and salt. Stir in the brown sugar, and oats. Add the butter, and using your fingertips, work the butter into the mixture until moist and crumbly.

Press half of the mixture into the prepared pan, and bake for 15 minutes until lightly browned. Spread the strawberry mixture on top, then sprinkle with the remaining crumb mixture.

Bake for 30 - 35 minutes, or until golden brown. Allow to cool completely in the pan on a wire rack before cutting into bars.