Pour oil into a large, deep saucepan. Place over medium-high heat. Once hot, carefully lower vegetables, except beetroot, in batches, into the oil. Cook each batch for about 5 minutes or until golden. Remove with a slotted spoon, allowing excess oil to drip off, and place onto a wire rack. Cook beetroot last to prevent discolouring the oil and the other vegetables. Sprinkle with sea salt flakes and leave to cool.