Slice the courgettes thinly lengthways into long ribbons. Drizzle with oil and season with salt and pepper. Heat a griddle pan to very hot and grill the courgettes in batches until marked by the griddle on both sides, then place in a large salad bowl.
Make the dressing by whisking together the oil and the grated lemon rind and juice. Season to taste with salt the pepper.
Roughly chop the mint, reserving some leaves for garnish. Carefully mix together the courgettes, mint and dressing. Transfer them to a large salad bowl, then crumble the feta over the top, garnish with the remaining mint leaves and serve.