Preheat the oven to Gas Mark 4, 180˚C (356˚F)
Line the bottom of a 20cm square baking tin with parchment paper and spray with cooking spray for easy removal.
In a large bowl, combine the melted butter, flours, oats, honey, brown sugar, cinnamon and salt. Mix until just combined and crumbly. Scoop out around one third of the mixture and set aside for the topping.
Spread the remaining mixture into the bottom of the prepared tin, using your fingers to press it into an even layer.
For the filling, place the strawberries in a bowl and toss with the lemon juice, vanilla extract and flour.
Spread the strawberry mixture evenly over the base. Scatter the reserved crumble mixture over the top.
Bake for 50 minutes until golden brown on top. Allow to cool in the tin, then carefully remove and allow to cool for another 10 minutes. Slice into 12 bars.