Strip the leaves from the bottom 2/3 of the rosemary stalks (use the leaves in other recipes). The stalks are now ready to use as a skewer.
Toss the mozzarella with the olive oil, pesto and balsamic vinegar. Season and leave to marinate for at least 30 minutes.
Trim the ends off the courgettes and peel into long strips using a vegetable peeler. Wrap a piece of courgette around each of the mozzarella balls and thread onto the rosemary stalk along with a cherry tomato and an olive. Brush any remaining marinade over the courgettes. Chill until you’re ready to cook them.
Heat a griddle pan and sear the skewers for a minute or so each side so that the cheese begins to soften, but doesn’t melt. Serve with a sprinkle of flaked sea salt and black pepper.