Take half a dozen bamboo skewers and soak them in a bowl of cold water for half an hour. (This prevents them from burning so quickly when they are put on the BBQ.)
Meanwhile, wash and slice two large courgettes (or three smaller ones) into chunks about 2cms on a side. Peel three small red onions and slice into quarters. Halve a lime, and cut a single thin slice from each of the halves, then squeeze the juice from the remaining pieces. Finely slice a small red chilli, and remove the seeds.
In a glass jar with a lid (use one which had previously been used for pickles or somesuch), put the sliced chilli and the lime juice. Add 6 tablespoons of olive oil, a tablespoon of light soy sauce, a little salt and lots of freshly-ground black pepper. Put on the lid and shake vigorously to mix.
Thread the courgette pieces and the onion quarters alternately onto the skewers. You should be able to get three or four pieces of courgette and two or three pieces of onion on each skewer.
Place the loaded skewers into a flat dish and pour the marinade over the top, making sure every part of the vegetables are coated. Garnish with the lime slices and some fresh herbs (optional) - I usually use sage and finely chopped chives. Cover the dish with clingfilm and put it in the fridge for an hour.
The barbecue should be at a medium heat for these skewers - not too hot. Cook for ten minutes or so, turning frequently, and pour a little of the left-over marinade over the vegetables from time to time.