Preheat the oven to 350?F (175?C). Grease the baking pan.

In a mixing bowl, combine flour, oats, brown sugar, melted butter, and salt. Mix until crumbly.

Press half of the mixture into the bottom of the prepared baking pan.

In another bowl, combine blackberries, granulated sugar, lemon juice, and cornstarch. Gently toss to coat the berries.

Spread the blackberry mixture evenly over the crust in the baking pan.

Sprinkle the remaining crumb mixture over the top of the blackberries.

Bake in the preheated oven for 25-30 minutes, or until the top is golden brown.

Allow to cool before cutting into bars. Serve warm or at room temperature.