Preheat your oven to 350F
In a small bowl, mix the mixed berries (along with their juices if using thawed frozen berries) with the white sugar.
In a separate medium-sized bowl, add the oats, flour, oat bran, brown sugar, cinnamon, salt, butter and olive oil. Mix to combine.
In a small 6.5” cast iron skillet or loaf pan, press half of the crumble mixture into the bottom of the pan. Top with the berry mixture, then scatter the remaining crumble mixture over top.
Place the skillet on to a larger sheet pan (to catch any spillage) and place into the oven.
Bake for 20 minutes or until the top is golden and the fruit filling is bubbling. Remove, let cool for 5 minutes.
Serve on its own or with a scoop of vanilla ice cream. Enjoy!