Make the dough by mixing oat flour, rolled oats, honey, extra virgin olive oil and vanilla extract together.
Reserve half of the dough for the crumble topping.
Press and lightly flatten the rest of the dough into a 20 x 20 cm tin and put it in the fridge.
To make the filling, put blueberries, honey, lemon juice and chia seeds together in a pot over medium heat, stir with a rubber spatula, cook for about 10 minutes, or until thickened.
Spoon the filling over the crust and evenly sprinkle the reserved oats on top.