Preheat oven to 160 degrees C (gas mark 2).

Line a 13 x 8 inch baking tin with parchment paper.

Combine rolled oats, flour, cinnamon, butter, and sugar in a mixing bowl.

Mix with a hand or stand mixer until a breadcrumb consistency is achieved.

Reserve a few tablespoons of oats for the topping.

Press two-thirds of the mixture into the prepared tin to form the base.

Blend raspberries, sugar, lemon juice, and cornflour until smooth.

Spread the raspberry mixture evenly over the base.

Stir the reserved oats into the remaining crumble mixture.

Sprinkle the crumble topping evenly over the raspberry filling.

Bake for 35-40 minutes, or until lightly golden.

Remove from the oven and mark into slices while still warm.

Let cool completely in the tin before serving.

Serve as a cake bar or with ice cream or custard.