Can be made earlier in the day. Slice the courgettes into halves lengthwise, or quarter 4 medium ones. Heat a little oil in a frying pan and put the courgettes in, cut-side down. Cook for 3 mins until lightly browned, then flip over and remove the pan from the heat. Stack the basil leaves on top of each other and slice thinly into shreds. Sprinkle the courgettes with a little more oil and scatter the black olives and the basil shreds. Marinate until cooled.