Whisk together the ingredients for the vinegar dip and set aside.
To make the batter, whisk the flour and a pinch of salt with 50ml/2fl oz cold water in a bowl until it forms a smooth paste.
Heat 1cm/½in of sunflower oil in a large, deep saucepan over a medium-high heat until it reaches 180C. The oil is hot enough when a cube of bread turns golden brown in around 15 seconds.
Add half of the courgettes to the batter and toss to coat. Gently lift them out using a slotted spoon, shaking off the excess batter.
Add the battered courgettes to the hot oil, spreading them out so they don't stick together. Fry for around 5 minutes, turning halfway. Transfer to a plate lined with kitchen paper whilst you batter and cook the remaining courgettes.
Sprinkle the courgette fries with sea salt and oregano, and serve with the vinegar to dip.